RESTful APIs (Representational State Transfer Application Programming Interfaces) are a set of rules and protocols that enable communication between web applications and servers over the internet. They are widely used in web development to create scalable, flexible, and maintainable systems.

The main purpose of RESTful APIs is to facilitate data exchange between the client (such as a web browser or mobile app) and the server in a stateless manner. This means each request from the client must contain all the necessary information for the server to process it, without relying on previous interactions. RESTful APIs typically use HTTP methods such as GET, POST, PUT, DELETE, and PATCH to perform operations on resources (data) stored on a server.

By separating the frontend and backend components, RESTful APIs allow developers to work on different parts of a web application independently. This makes the development process faster and more efficient, especially when dealing with complex applications. REST APIs are also language-agnostic, meaning they can be consumed by any programming language that supports HTTP, making them highly versatile.

To work effectively with RESTful APIs and build modern web applications, it's essential to learn full stack web development.