The straight punch with the lead hand — the most-used punch in boxing and the basis of nearly every combination.
The jab is rarely the punch that lands and ends things — it's the punch that sets everything up: measuring distance, occupying your opponent, building your cross. Technically it goes straight out from the guard, the shoulder rotating with it to shield the chin, and the hand returns along the same path. That return is the weak point: nearly every beginner drops the hand after jabbing and eats the counter right. The second typical error is punching from the shoulder instead of the ground — even the jab draws power from footwork and hip rotation, not the arm. And the rear hand stays on the chin, always.