As of .NET 3.0, LINQ (and the often related Lambda Expressions) have been available for our use and abuse. LINQ stands for Language INtegrated Query, and is a method of modelling OO data in a more or less relational sense that is not unlike databases. And just like databases, it comes with a cost.

To offset this cost, LINQ uses Deferred Execution. Deferred Execution means that the code is not executed until it is needed. This means that the LINQ code that you write is not actually executed until you NEED to execute it – typically during an enumeration of the results.