architecture - What's the difference between REST & RESTful

Question

What's the difference between a REST system and a system that is RESTful?

From a few things I've read most so called REST services are actually RESTful services. So what is the difference between the two.

Answer 1

Representational state transfer (REST) is a style of software architecture. As described in a dissertation by Roy Fielding, REST is an "architectural style" that basically exploits the existing technology and protocols of the Web.

RESTful is typically used to refer to web services implementing such an architecture.