If something's mid, it's just okay at best, nothing special and kind of disappointing. People use it to throw light shade at food, movies, music, or pretty much anything that got hyped up but didn't deliver.
Everyone said that burger place was amazing, but honestly it was mid.
Rizz is your game with people you're into: the charm and smooth talk that makes someone want to date you or hook up with you. If you can flirt easily and get someone's number, you've got rizz. It probably comes from shortening "charisma."
He walked up to her at the party and got her number in two minutes, the guy has serious rizz.