REST

Concept

REST was invented by Roy Fielding. REST provides guidance on how to implement web application interfaces to the web. Typically, one says a web application is constructed in a REST-like way or not. REST is often associated (or implemented) with HTTP, but it could be implemented with other technologies too. REST is platform and language independent.

Resource – A logical resource is any concept (car, dog, user, invoice…) which can be addressed and referenced using a global identifier. Typically, each resource is accessible with a URI when implementing REST over HTTP (for example: http://www.mysite.com/invoice/34657).
Server – A logical server is where resources are located, together with any corresponding data storage features. Such servers do not deal with end user interfaces (GUI).
Client – Logical clients make requests to logical servers to perform operations on their resources. For example, a client can request the state of the resource, create a resource, update a resource, delete a resource, etc… Clients do not possess resources or corresponding data storage features. However, they deal with end user interfaces (GUI).
Request and Responses – The interactions between client and servers is organized with requests from client to server, and responses to requests from server back to client. Requests can contain representations of the resource.
Representation – A representation is a document representing the current status of a resource. It can also be the new desired status when a client makes a request to update a resource, for example.