In my previous Extension Methods blog post, I demonstrated how you could declare a simple "Person" class like below:

Listing 1

I then showed how you could instantiate a List<Person> collection with values, and then use the new "Where" and "Average" extension methods provided by LINQ to return a subset of the people in the collection, as well as compute the average age of people within the collection:

Listing 2

The p => expressions highlighted above in red are Lambda expressions.  In the sample above I'm using the first lambda to specify the filter to use when retrieving people, and the second lambda to specify the value from the Person object to use when computing the average.