REST (REpresentational State Transfer) is an architectural style, and an approach to communications that is often used in the development of Web services.

The use of REST is often preferred over the more heavyweight SOAP (Simple Object Access Protocol) style because REST does not leverage as much bandwidth, which makes it a better fit for use over the Internet. The SOAP approach requires writing or using a provided server program (to serve data) and a client program (to request data).

REST, which typically runs over HTTP (Hypertext Transfer Protocol), has several architectural constraints:

1. Decouples consumers from producers

2. Stateless existence

3. Able to leverage a cache

4. Leverages a layered system

5. Leverages a uniform interface

References :
1. http://searchsoa.techtarget.com/definition/REST
2. https://en.wikipedia.org/wiki/Representational_state_transfer