I came across a few of these. I understand that the longer item is the extender socket where one plugs in a GPU, and the little items with gold fingers go into the motherboard, and the two are connected together with a USB3 cable (not shown). Just curious what category each of these would fall under? I realize it would take a lot to make for much weight...thanks in advance.

The board with the large socket. I would submit it as Backplane. That's assuming the socket has gold contacts. The smaller boards. I would submit them as Connector Ends. Hopefully a more experienced escrapper will post.
But. That's what I would do.
Here to learn like everybody else.