What is a "Friendless Class" in C#? I heard someone refer to it but I googled it online and found nothing.

Well in C++ (as opposed to C#) a friend of some class C is a class or function which is not a member of C but is given access to C's private or protected members.

A friendless class is therefore a class which has no friends.

C# has no correspoding concept but it does support friend assemblies which are assemblies which are given access to the internal types of other assemblies using the InternalsVisibleTo attribute.

However, I have never heard of anyone referring to an assembly as friendless :)