REST is an architectural style where stateless servers provide representations of resources under its control. Client applications use known information about the representation content type to decide how to operate.
REST uses HTTP to fetch, update and delete resource representations.
In combination with HTTP it is the content types and the semantics associated with these that drive the application. The ATOM publishing protocol is a good example of a RESTful technology where given a single entry URL and knowledge of the content types and client can reliably interact with any ATOM server