C# LINQ Keywords - The where Clause and Filters

Following one or more from clause generators or the join clauses if there are any, you typically place one or more filter clauses. Filters consist of the where keyword followed by a predicate expression. The where clause is translated into a call to the Where extension method, and the predicate is passed to the Where method as a lambda expression. Calls to Enumerable.Where, which are used if you are performing a query on an IEnumerable type, convert the lambda expression into a delegate. Conversely, calls to Queryable.Where, which are used if you perform a query on a collection via an IQueryable interface, convert the lambda expression into an expression tree.

Source Of Information : Apress Accelerated C Sharp 2010