A **jack** is a small flag flown from a jackstaff at the bow of a warship when at anchor or alongside, to indicate the vessel’s nationality independently of the ensign at the stern. Jacks are often distinctive national designs different from the ensign. The naval term is also extended to small bow flags on civilian vessels.
**Example**: The Union Jack, when so used, takes its name from its function as the jack of British warships.
**See also**: [ensign](/glossary/ensign/), [jack-at-bow](/glossary/jack-at-bow/), [burgee](/glossary/burgee/), [courtesy-flag](/glossary/courtesy-flag/)