In computing, Representational State Transfer (REST) is the software architectural style of the World Wide Web. REST gives a coordinated set of constraints to the design of components in a distributed hypermedia system that can lead to a higher-performing and more maintainable architecture.

To the extent that systems conform to the constraints of REST they can be called RESTful. RESTful systems typically, but not always, communicate over HTTP with the same HTTP verbs (GET, POST, PUT, DELETE, etc.) which web browsers use to retrieve web pages and to send data to remote servers. REST interfaces with external systems using resources identified by URI, for example /people/tom, which can be operated upon using standard verbs, such as DELETE /people/tom.

Source and more information at https://en.wikipedia.org/wiki/Representational_state_transfer