REST stands for Representational State Transfer. It is an architectural style for implementing web services.
It is an API implementation that follows the REST architectural constraints. This provides an interface between client and server. The communication between client and server happens over HTTP.
As we know that HTTP is an stateless protocol, the REST API communication is also stateless as it uses HTTP.
Every time client sends a request to server - it has to go through the authentication and authorization process. Backend server exposes an API endpoint which is called by the client.
These REST API endpoints are key to implement a decoupled architecture. (Decoupling of Client and Backend service)
The REST-API is a single entry point for the system. It takes care of authentication, authorization and other necessary tasks before providing access to the application resources.