What does it mean for an API to be stateless?

When an API is described as stateless, it means that each API call is independent and contains all the necessary information for the server to fulfill the request. This design implies that the server does not store any information about the client's state between requests. Each request from the client must include all the context required for the server to process it, which promotes scalability and simplifies server design.

This statelessness is a fundamental principle of RESTful APIs, allowing them to handle multiple requests efficiently without needing to keep track of the user's previous interactions. Because the server does not need to manage session data, it can respond to requests more quickly and efficiently, making it easier to scale applications to handle a large number of concurrent users.