What are the main HTTP methods used in REST APIs, and what does each represent?

GET retrieves a resource without side effects (safe and idempotent); POST creates a new resource or triggers a non-idempotent action; PUT replaces an entire resource with the given representation (idempotent — calling it twice with the same body has the same effect as once); DELETE removes a resource (idempotent). Correctly matching intent to verb is what makes an API behave predictably for clients, caches, and retry logic.