Jack can have several meanings.

For electrical connectors, see Jack (connector).

In English language-speaking nations, Jack is a popular name for males. Jack is often seen as a nickname for John, although it can be a first name in its own right, especially in the United Kingdom.

In playing cards, the Jack is the lowest of the face cards and 11th in games that rank the Two (deuce) as lowest and Ace 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 flag used to identify the nationality of a ship's home port. It is usually a smaller version of the national flag with a modified design.

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