What did David Hoffman (Bankless host) mean by this?

"I don't take opinionated positions very often, I usually just buy eth, but I did put eth into compound, borrow bitcoin, bought more eth, put that back into compound to [inaudible] the merge."

Link: https://www.youtube.com/watch?v=lHxVRuUHJoA&t=3586s

What did he mean by 'compound'? Why borrow btc to buy eth?