Branching was adding on to another project and publishing it. Like COAN said, there was a branch count before, but they don't have it anymore... 🤷🏻♀️
Remixing I guess is the same thing, but sometimes you don't add anything.
Rehopping was like a shoutout to the project. You remixed the project (didn't add anything to it) and wrote REHOP in the title to show that you like it and advertise it too.
Now we mostly just use remixing as a general idea.