Functional Strategy Pattern
Another pattern that is widely used in Object Oriented world. And as far as .Net world is concern it is may be most used pattern in wide range of .Net API. And it heavily used in heavily used LINQ API.
So, I guess giving a understanding of that is kinda waste of space. Have a look at C# code.
People familiar with LINQ and lovers of Lambda will definitely argue that this is can be replaced by delegates.