You can find the detailed information on REST at http://www.ibm.com/developerworks/webservices/library/ws-restful/.
Your interest may be on How to expose CRM contents in the form of REST(oData) services?..
"SAP NetWeaver gateway" will help you on that. Details you can find it at http://scn.sap.com/community/netweaver-gateway
Now REST is a broad term and pattern. SAP implements it using NetWeaver gateway. Google s known to favour REST services with JSON techniques. You would do well to check google's REST webservices in their APIs for places, location searches and others.
When it comes to SAP its only Gateway (oData) as others have said. From a MBO perspective it is the same as webservice or RFC. oData comsumption through MBOs is on its way.