What is that IGrouping result returned from group by LINQ queries?

I dont know how much you people use LINQ but for me it was like a blessing. Since I figured out how helpful it is I never really looked back. But this post is not about obvious usefulness of LINQ, everyone should know that by now!!! I would like to clarify some exotic details on the results we get from group by queries with LINQ and explain a little bit more on that infamous IGrouping collection.