What Is Software: Definition, Types, Examples & Complete Guide Explained

Software is a fundamental component of modern computing systems. At its core, software can be defined as a collection of instructions, commonly known as programs, that direct a computer to perform specific operations and tasks based on user commands. Unlike hardware, which refers to the physical components of a computer, software represents the intangible aspect — the code and data that enable hardware to function effectively.

The instructions contained in software are written in programming languages and ultimately translated into binary code — a series of ones and zeroes — that the computer’s processor can interpret and execute. Every task a user intends to perform on a computer, from opening a file to browsing the internet, depends heavily on software.

Software exists in many forms and serves a wide range of purposes. Its primary function is to enable the computer system to operate in a way that aligns with human needs, automating processes and facilitating interaction with hardware.

The Role of Software in Computing Systems

Software serves as an intermediary between the user and the hardware components of a computer. While hardware executes the physical processing, software provides the logical instructions and user interface to control these operations. The relationship between hardware and software is symbiotic — hardware needs software to perform tasks, and software requires hardware to function.

Without software, hardware is essentially useless. A computer’s processor, memory, and storage devices cannot operate independently without a set of instructions guiding them. Software ensures that hardware resources are efficiently utilized and that users can interact with the system in an accessible manner.

Types of Software

Software can be broadly classified into three major categories based on its function and purpose:

• System Software

• Application Software

• Programming Software

Each of these categories plays a distinct role in the computing environment.

System Software

System software is the foundational software that manages computer hardware and provides an environment for application software to run. It operates continuously in the background and ensures that hardware components function cohesively with the operating system and applications.

Operating System

The operating system (OS) is a type of system software that manages hardware resources and provides common services for application programs. It acts as a bridge between the user and the hardware. Popular operating systems include Windows, macOS, Linux, iOS, and Android.

The OS manages tasks such as memory allocation, process scheduling, input/output operations, file management, and security controls. It enables users to execute programs without needing detailed knowledge of the hardware.

Device Drivers

Device drivers are specialized system software components that control and operate hardware devices connected to a computer. They provide a software interface to hardware devices such as printers, graphics cards, and network adapters, enabling the operating system and applications to use these devices without knowing their internal workings.

Each hardware device requires a compatible driver to function properly. Drivers translate generic commands from the OS into device-specific instructions.

Firmware

Firmware is permanent software programmed into a hardware device’s read-only memory (ROM). It provides low-level control for the device’s specific hardware. Unlike other software, firmware remains intact even when the device is powered off.

Examples of firmware include the BIOS (Basic Input/Output System) in computers, which initializes hardware during the startup process before handing control over to the operating system.

Utility Software

Utility software includes programs designed to help analyze, configure, optimize, and maintain the computer system. These tools assist with system diagnostics, disk management, antivirus scanning, file compression, and backup operations.

Common examples include disk cleanup utilities, antivirus software, file archivers, and system monitors.

Application Software

Application software is designed to help users perform specific tasks beyond the basic functioning of the computer. These programs directly serve user needs and can range from productivity tools to entertainment and communication applications.

Word Processors

Word processors allow users to create, edit, format, and print text documents. These applications provide various tools for document layout, spell-checking, and multimedia insertion.

Examples include Microsoft Word, Google Docs, and LibreOffice Writer.

Database Software

Database management software enables users to create, manage, and manipulate databases. These applications help store large volumes of data, retrieve information efficiently, and maintain data integrity.

Popular database software includes MySQL, Oracle Database, Microsoft SQL Server, and PostgreSQL.

Multimedia Software

Multimedia software provides tools for creating, editing, and playing audio, video, and images. These programs are vital for graphic design, video production, animation, and music creation.

Examples include Adobe Photoshop, Adobe Premiere Pro, CorelDRAW, and VLC Media Player.

Web Browsers

Web browsers allow users to access and navigate the internet by retrieving, displaying, and managing web content. They translate web addresses into readable pages and support multimedia and interactive content.

Common browsers include Google Chrome, Mozilla Firefox, Microsoft Edge, Safari, and Opera.

Freeware

Freeware is software distributed free of charge for unlimited use. While free, freeware may come with embedded ads or limitations in functionality. It is often used as a promotional tool by developers.

Examples include Skype, Zoom (basic version), Adobe Acrobat Reader, and VLC Media Player.

Shareware

Shareware is software distributed on a trial basis, allowing users to test the software before purchasing a full license. It typically has limited functionality or a time restriction.

Examples include WinRAR, Adobe Acrobat Pro (trial), and some antivirus programs.

Open-Source Software

Open-source software is released with its source code available to users. This allows users and developers to modify, enhance, and distribute the software freely. Open-source promotes collaboration and transparency.

Popular open-source software includes Linux, Apache HTTP Server, Mozilla Firefox, and LibreOffice.

Programming Software

Programming software consists of tools that developers use to create, test, and maintain other software. This category supports the software development lifecycle and enables coders to transform human-readable code into executable programs.

Compilers

Compilers convert high-level programming languages into machine code that a computer’s processor can execute directly. This transformation allows written code to be run on hardware without requiring further interpretation.

Examples of compilers include GCC (GNU Compiler Collection), Microsoft Visual C++, and Java Compiler.

Debuggers

Debuggers are essential tools for identifying and resolving errors or bugs in code. They allow developers to step through their programs, monitor variable values, and detect logical or runtime errors.

Examples include GDB (GNU Debugger) and Visual Studio Debugger.

Linkers

Linkers combine various compiled program files into a single executable file. They resolve references between different modules, enabling the program to run independently from the development environment.

Malware

Malware refers to malicious software designed to disrupt, damage, or gain unauthorized access to computer systems. Examples include viruses, worms, ransomware, and trojans.

Effective cybersecurity software is required to detect and prevent malware attacks to safeguard data and system integrity.

How Software Works: From Input to Output

Software operates by taking user commands or inputs and processing them to produce desired outputs. This process involves multiple stages:

1. User inputs data or commands through an interface.

2. The software converts these instructions into binary code understandable by the computer.

3. The processor executes the instructions, interacting with hardware components as necessary.

4. The software generates output based on the processing results, which is then presented to the user.

The input can vary widely, from keystrokes, mouse clicks, or sensor data to files and network communications. Software interprets these inputs, performs logical operations, calculations, or data manipulation, and delivers meaningful results.

For instance, when you open a document in a word processor, the software reads the file from storage, interprets the data, renders the text and graphics on the screen, and allows you to edit the content. When you save the file, the software converts the edited data back into a storable format.

This foundational understanding sets the stage for exploring further aspects of software, such as distribution methods, design and implementation, maintenance, and licensing, which will be covered in subsequent parts.

Software Distribution: How Software Reaches Users

Software distribution refers to the various methods by which software is delivered from developers to users. The approach taken often depends on the software’s purpose, licensing, and business model. Understanding software distribution is crucial as it affects accessibility, usability, and legal considerations for users and organizations.

Commercial Software Distribution

Commercial software distribution involves selling licenses to users, granting them the right to use the software under specific terms and conditions. The users do not own the software itself but are allowed to use it according to the license agreement.

Typically, commercial software is sold through physical media like DVDs or via digital downloads. The license may restrict copying, modifying, or redistributing the software. Updates and support may be provided as part of the purchase or through separate maintenance agreements.

Commercial distribution was the dominant model in the early decades of software but has seen some decline with the rise of open-source and subscription-based models.

Open-Source Software Distribution

Open-source software is made available freely with its source code accessible for anyone to view, modify, and distribute. This model encourages collaboration among developers and allows users to tailor the software to their specific needs.

Distribution of open-source software typically occurs via online repositories and version control platforms like GitHub or GitLab. Open-source licenses, such as the GNU General Public License (GPL), define how the software can be used and shared, often requiring derivative works to also be open-source.

Open-source software can be offered for free, but some projects also sell services such as support, training, or customized versions.

Freeware Distribution

Freeware is software provided at no cost to the user, typically without access to the source code. It can be downloaded directly from websites or software platforms.

While freeware is free to use, developers may monetize it through embedded advertisements, offer paid upgrades, or provide premium features as part of a freemium model.

Freeware is often intended to attract users to a product line, increase brand recognition, or provide essential tools at no cost.

Shareware Distribution

Shareware allows users to try software free of charge for a limited time or with limited features. After the trial period expires, users must purchase a license to continue using the full version.

Shareware distribution enables potential customers to evaluate the software’s capabilities before committing financially. Common distribution methods include downloadable trial versions available on official websites or software distribution platforms.

Examples of shareware often include productivity tools, games, and utilities.

Software Design and Implementation

Creating software is a complex process that involves multiple stages, collectively known as the Software Development Life Cycle (SDLC). Proper design and implementation ensure the software meets user requirements, is maintainable, and functions reliably.

Requirement Analysis

Requirement analysis is the initial phase where developers work with stakeholders to understand what the software must achieve. This involves gathering detailed information about the intended functionalities, performance expectations, and constraints.

Clear documentation of requirements is critical to avoid misunderstandings and to guide subsequent design and development efforts.

Software Design

In the design phase, the software’s overall structure and components are planned. This involves defining system architecture, data models, user interfaces, and interaction flows.

Design decisions affect scalability, security, performance, and usability. Good design practices include modularization, separation of concerns, and adherence to design patterns that facilitate maintenance and future enhancements.

Implementation

Implementation involves writing the actual code based on the design specifications. Developers use programming languages and tools to build the software components.

During implementation, regular code reviews and adherence to coding standards help maintain quality. Developers also integrate different modules and prepare the software for testing.

Testing

Testing is a critical phase where the software is evaluated to detect and fix defects. Various testing types ensure the software functions correctly, securely, and efficiently.

Functional testing verifies that features work as intended. Non-functional testing assesses attributes like performance, usability, security, and compatibility.

Testing methodologies include unit testing, integration testing, system testing, and user acceptance testing.

Deployment

After thorough testing, the software is deployed to the production environment for use by end-users. Deployment may involve installation on user devices, uploading to cloud platforms, or distribution through app stores.

Deployment strategies, such as phased rollouts or continuous deployment, help manage risk and ensure smooth adoption.

Maintenance

Maintenance involves ongoing activities to fix bugs, improve performance, and add new features based on user feedback. Software maintenance is essential to extend the software’s useful life and adapt it to changing environments.

Maintenance tasks may include patching security vulnerabilities, updating dependencies, and optimizing code.

Maintaining Software Quality

Software quality is vital for user satisfaction, security, and long-term success. Maintaining quality involves continuous evaluation and improvement throughout the software’s lifecycle.

Functional Requirements

Functional requirements specify what the software must do — the core features and behaviors expected by users. Meeting these requirements ensures the software fulfills its intended purpose.

Non-Functional Requirements

Non-functional requirements define how the software performs its functions, including reliability, scalability, usability, security, and efficiency.

For example, a banking application must not only process transactions correctly (functional) but also protect sensitive data (non-functional).

Software Testing and Quality Assurance

Testing validates that both functional and non-functional requirements are met. Quality assurance (QA) teams establish processes and standards to prevent defects and ensure consistent software quality.

Testing tools automate many verification tasks, reducing human error and increasing coverage.

User Feedback and Continuous Improvement

User feedback plays a crucial role in identifying issues not caught during development. Agile and Lean development methodologies emphasize iterative improvements based on real-world use.

Regular updates and patches help address bugs, improve usability, and add features that align with user needs.

Modern Software Development Practices

Software development has evolved significantly, adopting methodologies that emphasize flexibility, collaboration, and customer focus.

Agile Methodology

Agile development promotes iterative cycles called sprints, where small increments of software are developed, tested, and delivered frequently. This approach allows rapid response to changing requirements and ongoing user feedback.

Agile teams prioritize communication, collaboration, and adaptability to deliver high-quality software quickly.

Lean Software Development

Lean principles focus on eliminating waste, optimizing processes, and delivering value efficiently. Lean encourages minimal overhead, continuous learning, and fast feedback loops.

Both Agile and Lean methodologies contribute to improved productivity, reduced risk, and enhanced customer satisfaction.

Software Licensing and Intellectual Property

Software licensing and intellectual property laws govern how software can be used, shared, and protected. Understanding these concepts is vital for developers, businesses, and users to ensure legal compliance and protect innovations.

What is Software Licensing?

Software licensing is a legal framework that defines the rights and restrictions related to the use and distribution of software. When users acquire software, they typically receive a license rather than ownership of the software itself.

Licenses specify how the software can be used, copied, modified, or redistributed. Violating license terms can lead to legal consequences, including fines or lawsuits.

Common Types of Software Licenses

Different licenses cater to various distribution models and user needs. The most common types include proprietary licenses, open-source licenses, freeware licenses, and shareware licenses.

Proprietary Licenses

Proprietary software licenses restrict usage to the terms defined by the software vendor. Users usually cannot modify, redistribute, or reverse-engineer the software.

Examples include commercial operating systems like Windows or applications like Adobe Photoshop. Proprietary licenses often require payment for use and limit installation to a specific number of devices.

Open-Source Licenses

Open-source licenses grant users freedom to use, modify, and redistribute software, often with certain conditions to maintain openness.

Popular open-source licenses include:

• GNU General Public License (GPL): Requires derivative works to also be open-source under the same license.

• MIT License: Permissive license allowing nearly unrestricted use and modification.

• Apache License: Permissive license that also provides explicit patent grants.

These licenses promote collaborative development and transparency.

Freeware Licenses

Freeware licenses allow free use but typically prohibit modification or redistribution. The source code is generally not available.

Freeware can be distributed with embedded advertising or limited functionality to encourage upgrades.

Shareware Licenses

Shareware licenses provide trial access to software, often for a limited time or with restricted features. Users are expected to purchase a full license for continued or full use.

This model helps developers monetize software while giving users a chance to evaluate it.

Intellectual Property Protection: Copyrights and Patents

Software is protected under intellectual property laws, primarily copyrights and patents, each serving different purposes.

Copyright Protection

Copyright protects the original expression of software code, preventing unauthorized copying or distribution. It does not protect the underlying ideas or functional aspects.

Copyright applies automatically once the software is created and fixed in a tangible form, though registration can enhance legal protections.

Patents in Software

Software patents protect specific inventions or functional aspects of software, such as unique algorithms or processes. Patents prevent others from using the patented methods without permission.

Patent laws vary by jurisdiction, and software patents can be controversial due to challenges in defining patentable software innovations.

Software License Agreements and Terms

Software licenses typically include detailed agreements outlining:

• Permitted uses and restrictions

• Number of authorized installations

• Limitations of liability and warranties

• Conditions for updates and support

• Intellectual property rights

• Termination clauses in case of breach

Users should carefully review these agreements before installation to avoid unintended violations.

History and Evolution of Software

The history of software traces its development from early computing machines to today’s complex systems. Understanding this evolution provides context for modern software concepts and practices.

Early Beginnings of Software

In the 1940s and 1950s, software as a concept was not yet formalized. Programs were written in machine language, directly controlling hardware.

The first recognized software was written in 1948 by Tom Kilburn at the University of Manchester. The term “software” was coined by John Tukey in 1958.

Commercial Software Emergence

In the 1970s and 1980s, commercial software began to take shape with companies like Microsoft and IBM selling software products.

The release of personal computers expanded software markets, and applications like word processors and spreadsheets became popular.

Advancements in Operating Systems

Operating systems evolved to support multitasking, networking, and graphical user interfaces. Notable milestones include:

• Microsoft Windows (1985)

• Apple Macintosh System Software

• Unix and Linux development

These advances made computers more accessible and user-friendly.

Software Delivery and Distribution Changes

Initially, software was distributed on physical media such as floppy disks and CDs. The rise of the internet enabled online downloads and updates, reducing distribution costs and increasing accessibility.

The introduction of cloud computing and Software as a Service (SaaS) transformed delivery models, enabling on-demand access and subscription services.

Mobile and Modern Software Era

The launch of smartphones, starting with the first iPhone in 2007, ushered in a new era of mobile applications and app stores.

Modern software development embraces agile methodologies, continuous integration, and deployment, responding quickly to user needs and technological advances.

Malware: Understanding Malicious Software

Malware, short for malicious software, is designed to harm or exploit computer systems. Recognizing types of malware and how they operate is essential for maintaining software security.

Types of Malware

Malware comes in various forms, each with different objectives and methods of attack.

Viruses

Viruses attach themselves to legitimate programs and spread by executing malicious code when the host program runs. They can corrupt files, delete data, or disrupt operations.

Worms

Worms are self-replicating malware that spread across networks without user intervention, often causing widespread disruption.

Trojans

Trojans disguise themselves as legitimate software but contain harmful payloads, such as backdoors for unauthorized access.

Ransomware

Ransomware encrypts user data and demands payment to restore access. It has become a major cybersecurity threat for individuals and organizations.

Spyware and Adware

Spyware collects user information without consent, while adware displays unwanted advertisements, sometimes bundled with free software.

Malware Prevention and Protection

Protecting software and systems from malware involves:

• Installing and regularly updating antivirus and anti-malware software

• Applying security patches and updates promptly

• Avoiding suspicious downloads and email attachments

• Using firewalls and intrusion detection systems

• Educating users about safe computing practices

Maintaining software quality and security is an ongoing effort in today’s interconnected environment.

Software Development Lifecycle (SDLC)

Software development is a structured process that guides the creation, deployment, and maintenance of software. The Software Development Lifecycle (SDLC) provides a framework to plan, build, test, and deliver high-quality software efficiently and effectively.

Phases of the Software Development Lifecycle

The SDLC consists of several distinct phases, each with specific goals and deliverables. These phases ensure that software development aligns with user requirements, quality standards, and business objectives.

Requirement Analysis

Requirement analysis is the first phase where the needs and expectations of the users and stakeholders are gathered and documented. This involves detailed discussions to understand what the software should achieve.

Key activities include:

• Gathering functional and non-functional requirements

• Prioritizing features and functionalities

• Identifying constraints and risks

• Creating requirement specification documents

Effective requirement analysis prevents misunderstandings and scope creep during later phases.

Planning

Planning involves outlining how the project will proceed, estimating timeframes, costs, and resource allocation. Project managers develop schedules, assign roles, and identify tools and technologies.

A solid plan balances scope, time, and cost to ensure feasibility and sets milestones for progress tracking.

Design

During the design phase, the system architecture and detailed design specifications are created. This includes:

• Defining system components and their interactions

• Designing user interfaces and experience (UI/UX)

• Database schema design

• Security and performance considerations

Design documents guide developers and testers throughout the implementation phase.

Implementation (Coding)

Implementation is the phase where developers write the actual code according to design specifications. This involves:

• Writing source code using programming languages

• Following coding standards and best practices

• Version control and collaborative development

Code quality during implementation is crucial for maintainability and scalability.

Testing

Testing ensures that the software functions correctly and meets requirements. Different testing methods are applied to identify bugs, errors, and performance issues.

Common testing types include:

• Unit Testing: Verifies individual components or functions

• Integration Testing: Ensures components work together

• System Testing: Tests the complete system for compliance

• Acceptance Testing: Validates software against user requirements

Automated testing tools and manual testing both play important roles.

Deployment

Once tested, the software is deployed to the production environment where users can access it. Deployment can be a straightforward installation or a complex rollout involving multiple environments.

Key considerations include:

• Minimizing downtime

• Ensuring data migration and backup

• Monitoring initial performance

Continuous deployment practices enable frequent, incremental releases.

Maintenance and Support

Software maintenance involves updating and improving software after release. This includes:

• Bug fixes and patches

• Performance enhancements

• Adapting to changing user needs

• Adding new features

Ongoing support ensures software remains functional, secure, and relevant over time.

Importance of SDLC

Following an SDLC framework reduces risks, improves project visibility, and promotes better collaboration among teams. It ensures a systematic approach to software development, leading to higher quality products delivered on time and within budget.

Modern Software Development Methodologies

Traditional waterfall SDLC models have evolved to more flexible and iterative approaches that accommodate changing requirements and faster delivery.

Agile Methodology

Agile is an iterative approach emphasizing collaboration, customer feedback, and rapid delivery. Agile divides work into small cycles called sprints, usually lasting 2-4 weeks.

Key principles of Agile include:

• Continuous delivery of functional software

• Close collaboration between developers and stakeholders

• Responding to change over following a fixed plan

• Self-organizing cross-functional teams

Popular Agile frameworks include Scrum and Kanban, each with specific roles, ceremonies, and workflows.

DevOps

DevOps integrates development and operations teams to improve collaboration and automate software delivery. It focuses on:

• Continuous Integration (CI): Frequent merging of code changes into a shared repository

• Continuous Delivery (CD): Automated deployment of tested code to production or staging environments

• Infrastructure as Code (IaC): Managing infrastructure through code and automation

DevOps practices accelerate release cycles and improve reliability.

Lean Software Development

Lean development focuses on eliminating waste, improving efficiency, and delivering value quickly. It adapts Lean manufacturing principles such as:

• Delivering fast and often

• Optimizing the whole development process

• Empowering teams to make decisions

• Emphasizing quality from the start

Lean complements Agile and DevOps by promoting streamlined workflows.

Feature-Driven Development (FDD)

FDD is an iterative and incremental development process driven by client-valued features. It involves:

• Developing an overall model

• Building a feature list

• Planning by feature

• Designing and building features in small, manageable units

FDD promotes regular progress tracking and clear client involvement.

Software Quality Assurance (SQA)

Ensuring software quality is critical to delivering reliable and efficient products. Software Quality Assurance (SQA) encompasses all activities aimed at preventing defects and ensuring the software meets requirements.

Quality Attributes in Software

Software quality is measured by various attributes, including:

• Functionality: The software performs its intended functions accurately

• Reliability: The software operates consistently without failures

• Usability: The software is easy to learn and use

• Efficiency: The software uses resources optimally

• Maintainability: The software can be modified and extended easily

• Security: The software protects data and resists unauthorized access

Balancing these attributes is essential to overall software quality.

Software Testing Techniques

Testing is a core part of SQA. Techniques include:

• Black Box Testing: Testing without knowledge of internal code, focusing on inputs and outputs

• White Box Testing: Testing with detailed knowledge of the internal structure

• Regression Testing: Retesting after changes to ensure existing features remain functional

• Load and Stress Testing: Assessing performance under heavy usage or extreme conditions

• Security Testing: Identifying vulnerabilities and risks

Automation tools enhance testing efficiency and repeatability.

Code Reviews and Static Analysis

Peer reviews and automated static code analysis tools help identify coding errors, enforce standards, and improve code quality before testing.

Continuous Monitoring

Post-deployment monitoring tracks software behavior in production, helping identify issues proactively.

Software Maintenance and Evolution

Software maintenance is an ongoing process necessary to keep software useful, relevant, and secure throughout its lifecycle.

Types of Software Maintenance

Maintenance tasks fall into categories:

• Corrective Maintenance: Fixing bugs or defects found after release

• Adaptive Maintenance: Updating software to work with new hardware or operating environments

• Perfective Maintenance: Enhancing functionality or performance based on user feedback

• Preventive Maintenance: Anticipating and preventing future problems

Challenges in Software Maintenance

Maintenance can be complex due to factors like:

• Lack of documentation

• Dependencies on outdated technology

• Changing user requirements

• Technical debt accumulation

Effective maintenance requires good planning and skilled personnel.

Software Reengineering

Sometimes software must be reengineered to modernize or improve it without complete redevelopment. This can involve:

• Reverse engineering legacy code

• Refactoring and restructuring

• Migrating to new platforms or languages

Reengineering extends software life and reduces redevelopment costs.

Future Trends in Software Development

Software development continues to evolve rapidly, driven by technological advances and changing user demands.

Artificial Intelligence and Machine Learning

AI is increasingly integrated into software to enable intelligent features such as:

• Natural language processing

• Predictive analytics

• Automated decision-making

Developers use AI tools to assist coding, testing, and debugging.

Cloud Computing and SaaS

Cloud platforms provide scalable resources and services, enabling software to be delivered as SaaS with easy access and flexible pricing.

Low-Code and No-Code Development

Low-code and no-code platforms allow users with minimal programming knowledge to build applications using visual interfaces, speeding up development.

Blockchain and Decentralized Applications

Blockchain technology supports secure, transparent software systems, especially in finance, supply chain, and digital identity.

Cybersecurity Focus

As cyber threats grow, software development increasingly integrates security from design to deployment, known as DevSecOps.

Internet of Things (IoT)

IoT software connects and manages vast networks of devices, requiring specialized development approaches for reliability and data handling.

Conclusion

Software is the backbone of modern technology, enabling users to interact with hardware and perform a vast range of tasks. From system software managing hardware to complex applications fulfilling diverse user needs, software comes in many forms and serves countless purposes.

Understanding software types, licensing, development processes, quality assurance, and future trends equips developers and users with the knowledge to create, maintain, and use software effectively. The software development lifecycle provides a roadmap for producing high-quality software, while modern methodologies like Agile and DevOps support faster, more responsive development.

Continuous evolution in software technologies and practices promises exciting advancements, making software development a dynamic and essential field in today’s digital world.