Jack can have several meanings:
- For electrical connectors, see Jack (connector).
- The web comic Jack.
- A jack is one of several types of mechanical device used to lift heavy objects, such as cars.
- In English-speaking nations, Jack is a popular name for males. Usually, Jack is a nickname for John.
- In playing cards, the Jack is the lowest of the face cards and 11th in games that rank the Ace as lowest and King as highest. The jack was originally called the Knave. In blackjack, the Jack has a value of 10.
- In naval and maritime terminology, a jack is a type of national flag flown from a jack staff at the head of a ship. It is usually only flown by naval vessels, although civilian jacks do exist. See Maritime flags.
- In William Golding's "Lord of the Flies" Jack is the name of the antagonist, head of a school choir, who by being an active but less practical leader, turns the other boys agains Ralph, their original leader on the island.
- In entertainment, Jack is a 1996 movie directed by Francis Ford Coppola, starring Robin Williams.
- The jack (also jak) is a species of tree (Artocarpus integrifolia ) native to the East Indies, used in cabinet making.
- In Military Rank, Master Jack refers to a Master Corporal or Master Seaman in the Canadian Armed Forces.
- Jack is the common name of several species of perciform marine fish in the family Carangidae .
- A jack or jackass is an entire male donkey.
- Jack, as a verb, is a common euphemism for masturbation.
- Jack A Jack-in-the-box.
- The JACK Audio Connection Kit is a low latency sound server.
- Slang for Jack Daniels brand whiskey.
