peel vs engage
Which way the spell points. Engage is throwing your crowd control at the enemy to start the fight; peel is saving it to protect a teammate. The same spell, two opposite uses.
peel
Peeling is pushing away or locking down the enemies who jump on a teammate, usually the carry. The tank who stays next to their marksman instead of charging in, the support who keeps their stun for the assassin: they are peeling. "peel for me pls" is the request of a carry who knows they are the target.
open the page →engage
Engaging is starting the fight: diving onto a target, landing your crowd control on the enemy team, forcing everyone to fight. It is the job of tanks and some supports. "we have no engage" in champ select means nobody on the team can do that.
open the page →Why they get mixed up
The same champion, with the same spells, can do either: it is a decision, not an ability. The confusion happens mid-fight, when the tank engages while the carry was asking for peel, and ends up alone in front while the marksman dies behind. "peel or engage" is a question to settle before the fight, not during.