You are it意思

"You are it" is a phrase often used in children's games, particularly in tag or chase games, where one player is designated as "it" and has to chase and tag other players. When a player is tagged, they become "it" and have to continue the game by chasing the other players.

So, when someone says "You are it," they are designating that person as the one who is now responsible for chasing and tagging others in the game.