What is Fstand for contained by motherboard?

What is Fstand for contained by motherboard?

Can't find it within my motherboards but lots of it in my keyboards. It technique Function and F1-F12 are the Function keys.
Did u expect keyboard?
Its the socket for your motherboard. For example Socket AM2, Socket 939, Socket F. If u want to upgrade your processor and RAM, make sure i will work next to socket F.