What is REST and RESTful web services?
REST was introduced as an architectural style for building large-scale distributed system. By "architectural style" we mean - a set of design rules that identify the kinds of components and connectors that may be used to compose a system or subsystem.
REST is the stateless client-server architecture in which resources are exposed as web service and can be identified by their URL's/URI's. By using set of remote methods client can use the resources and in return web service returns representational state of the resource.
RESTful is typically used to refer to web services implementing such an architecture.