The REST (Representational State Transfer) API for SharePoint is designed to give developers an alternative method to access the data that stored inside of SharePoint. It’s goal is to make SharePoint more ‘mash-able’.
Just as SharePoint can act as a SOAP service provider and client, so it can act as a REST service provider and client. This lets you use SharePoint Designer to create solutions that
consume XML data from REST services, including XML data retrieved from SharePoint REST interfaces. The number of SharePoint REST interfaces is small compared to the number of
SharePoint SOAP service interfaces. The two SharePoint 2010 REST interfaces are
-ListData.svc Provides access to list and library data.
-ExcelRest.aspx : Allows for easy discovery of and access to data and objects within a spreadsheet. (Enterprise only)