What is PLUS times PLUS?

I'm so bad at billiards that I ended up in the hyperbolic plane [video]

“This entire youtube channel is a gem btw. Delightful video on the lambda calculus and other compution concepts https://www.youtube.com/watch?v=RcVA8Nj6HEo”— ChrisbyMe, when sharing this video · read the comment ↗