Hypermedia as the Engine of Application State (HATEOAS) is a fundamental constraint in RESTful architecture for APIs. It refers to the principle of including hypermedia links in the API responses to guide clients dynamically through available actions. The API acts as a navigable web of resources interconnected by hyperlinks, allowing clients to discover and interact with resources without prior knowledge of their structure or endpoints.
This feature promotes a decoupled and flexible design, thereby enabling the server to evolve independently while maintaining backward compatibility. HATEOAS enhances the scalability, discoverability, and adaptability of REST APIs, making it a crucial element in building truly RESTful systems.