What is my seal called?

Thanks for all the help guys. I think it is fixed. I did what was told here.
The hardest part was getting the old seal out.
I left it on jack stands, with the rear end "high" in the air, and left it run in drive for about 10 minutes. No leaking now.
Unless it does it after driving?
It used to just drip while sitting level. There was a constant slow drip.
I don't have the interior in right now, so no test drive.
I would think it would drip while the wheels were turning there on jack stands.
They were rolling pretty quick. It even hit second gear while running it like that. Nice and dry!