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API (Application Programming Interface)

A set of rules for software interaction.

Business Glossary provided by

An API is a framework that enables different software systems to communicate with each other, allowing the integration of separate software components or services. It defines the correct way for a developer to write a program that requests services from an operating system or other application. APIs are used in all kinds of software development and are critical for creating complex systems and platforms that rely on multiple software components working together.

Context of Use:

An API (Application Programming Interface) is a set of protocols, routines, and tools for building software applications. It specifies how software components should interact and can be used when programming graphical user interface (GUI) components, connecting different software systems, or accessing web-based services. APIs are essential for facilitating the seamless operation and integration of different software systems, allowing them to communicate and share data efficiently.


The purpose of an API is to allow an application to expose a specific set of services or data to other applications, while maintaining security, control, and abstraction. This enables developers to use functionalities that are provided by another service without needing to understand the underlying codebase fully. APIs are crucial for developing modular, scalable, and maintainable software.


Consider a travel booking website that uses APIs to retrieve real-time data from various airlines, hotels, and car rental services. When a user searches for a flight, the website uses an API to query airline databases to fetch flight options without needing direct access to their internal systems. This allows the website to aggregate data from multiple sources and provide a comprehensive set of options to the user.

Related Terms:

  • REST (Representational State Transfer): An architectural style for designing networked applications that use a stateless communication protocol, typically HTTP. RESTful APIs are designed around standard HTTP verbs (GET, POST, PUT, DELETE) and URIs (Uniform Resource Identifiers).

  • SOAP (Simple Object Access Protocol): A protocol specification for exchanging structured information in the implementation of web services in computer networks. It relies on XML (Extensible Markup Language) for its message format.

  • JSON (JavaScript Object Notation): A lightweight data-interchange format that is easy for humans to read and write, and easy for machines to parse and generate. Commonly used for API responses.

  • Endpoint: In the context of APIs, an endpoint is a specific URL where an API can be accessed by a client application.


  1. How do APIs work?

    APIs work as an intermediary layer that processes requests and ensures seamless communication between different software systems. A client application makes a call to the API, the API processes the request, and then the API returns the appropriate response back to the client application.

  2. Why are APIs important for modern software development?

    APIs simplify software development and innovation by enabling applications to interact and share data. They allow developers to leverage existing platforms instead of building solutions from scratch, thus reducing development time and costs.

  3. What are public and private APIs?

    Public APIs (or open APIs) are available to developers and other users with minimal restrictions. They are intended to be shared with the external developer community. Private APIs, on the other hand, are used internally within an organization and are not exposed to external users.

  4. What is API throttling?

    API throttling is the practice of limiting the number of API requests a user can make in a given time period. This helps manage the load on the API server and ensures that it does not get overwhelmed by too many requests.

  5. How do developers secure APIs?

    Developers can secure APIs using methods such as HTTPS, token-based authentication, API keys, and OAuth. These methods ensure that only authorized users can access the API, protecting it from unauthorized use and attacks.

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