A jab is one of the three main punches used in boxing, the two others being the uppercut and hook. Out of all three, the jab is perhaps the most popularly known one, because the word is often used in talk unrelated to boxing. It is rarely the strongest punch in a fighter's arsenal. The Compubox computerized punch scoring system divides punches between jabs and power punches.

Jabs are long, arm-length punches usually thrown from a distance. They are used for many purposes. One of the most important uses of a jab is to set up the opponent for another punch. Jabs usually land on the face or the head, but jabs to the stomach are also effective. While a boxer receives a jab to the face, his rival might try to sneak in a more powerful, hook or uppercut, in this case, the jab is a set up and also works as a cover. Jabs can also be used to begin combinations, usually followed by the uppercut or hook, but jabs can also be thrown after the hook or uppercut. When a fighter is hurt, the jab usually becomes of second importance, as the opponent moves in for the knockout and throws harder punches.

Historians consider some of the best jabbers in history to be Sonny Liston, Larry Holmes, Muhammad Ali, Hector Camacho and Sugar Ray Leonard. Holmes' jab has often been called "the best among Heavyweights", while Ali's jab was famous for its speed.

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In American English, the word jab is also used when someone is bothering someone else, what is commonly known as verbal jabs. "Dont throw jabs at me" and "Quit jabbing!" are popular sayings.

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In British English, the word jab is also used to mean a medical injection.