Simple definition
An HTTP method identifies the requested operation on a resource, such as GET, POST, PUT, PATCH, or DELETE.
Purpose and use
An HTTP method expresses a request's intent toward a resource: retrieval, processing, replacement or deletion according to its semantics.
How does it work?
GET and HEAD are defined as safe; PUT and DELETE are idempotent. These properties concern intended effects, not absence of logging or identical responses.
Example and verification
When designing an API, verify that state-changing actions use methods and controls appropriate to their effects.
Points to watch
Changing the method name alone creates no access protection. The server must still enforce authentication, authorization and validation.
In short
Method semantics inform retry behavior, caching and protection against unwanted requests.