What is RESTFul Web Service

REST - Representational State Transfer

REST is an architecture style or design pattern used for creating web services.

RESTful Web services allow anything connected to a network (web servers, private intranets, smartphones, banking systems) to communicate with one another.

They communicate via a shared common communications protocol known as Hypertext Transfer Protocol (HTTP). 

The same HTTP verbs (GET, POST, PUT, DELETE etc.) used by web browsers 

 - to retrieve and display web pages, audio/video files, images etc. from remote servers and 

 - post data back to them when performing actions like filling out and submitting forms 

REST is used as a simpler alternative to SOAP and WSDL based Web services. 

For more understanding click here http://akash-java.blogspot.in/p/representational-state-transfer-rest-is.html