REST, or Representational State Transfer, is an architectural style used for designing networked applications, particularly web services. RESTful services rely on stateless, client-server communication where each request from a client to the server must contain all the information needed to understand and process the request. In REST, resources are identified by URLs (Uniform Resource Locators) and are manipulated through standard HTTP methods such as GET, POST, PUT, DELETE, etc. REST is known for its simplicity, scalability, and flexibility, making it a widely adopted standard for building APIs (Application Programming Interfaces) that are easy to integrate and maintain.

REST APIs are typically used to interact with web-based applications, where different systems need to exchange data or functionality. For instance, a RESTful API could allow a mobile app to retrieve user data from a web server, update user preferences, or delete content. RESTful services can return data in various formats, including JSON and XML, with JSON being the most popular due to its lightweight and easy-to-parse structure. The principles of REST have become the foundation for much of the web's interoperability, enabling developers to build scalable, efficient, and maintainable systems.