what is LINQ in C# ?

LINQ - Language Integrated Query is simply a unified programming model/framework for writing SQL queries in simple language(in which you are working for eg. C#,VB,etc) without learing SQL.Here unified programming model means once you write a LINQ query for a datasource that query will be fired/executed over different-different datasource.

For Example:

Linq To Sql query:

//
// var result=from m in DataContext.YourTableName select m;
//

This is simple Linq to Sql query for selecting a record from the database having table name "YourTableName"