frame 1

Is used to describe the quickness/hastiness of an action. In videos games, a hitbox appears at some point during a character's attack animation. Some attacks charge-up or go through several frames before the attack lands. Frame 1 is the quickest point at which an attack can come out causing instant damage and usually stun-locking. If a person says they are doing something "frame 1" it means they are doing it instantly.