REST is a style of software architecture that provides a convenient and consistent approach to requesting and modifying data.
The term REST is short for "Representational State Transfer." In the context of Google APIs, it refers to using HTTP verbs to retrieve and modify representations of data stored by Google.
In a RESTful system, resources are stored in a data store; a client sends a request that the server perform a particular action (such as creating, retrieving, updating, or deleting a resource), and the server performs the action and sends a response, often in the form of a representation of the specified resource.
In Google's RESTful APIs, the client specifies an action using an HTTP verb such as POST, GET, PUT, or DELETE. It specifies a resource by a globally-unique URI of the following form:
https://www.googleapis.com/apiName/apiVersion/resourcePath?parameters
Because all API resources have unique HTTP-accessible URIs, REST enables data caching and is optimized to work with the web's distributed infrastructure.
You may find the method definitions in the HTTP 1.1 standards documentation useful; they include specifications for GET, POST, PUT, and DELETE.