An ORM built by Microsoft and is available as part of .Net framework 3.5 and later.
ADO.NET Entity Framework abstracts the relational (logical) schema of the data that is stored in a database and presents its conceptual schema to the application. This abstraction eliminates the object-relational impedance mismatch that is otherwise common in conventional database-oriented programs.
Read more about it in MSDN : http://msdn.microsoft.com/en-us/library/bb399572.aspx