JACK, in the sea-language, a sort of flag or colours, displayed from a mast erected on the outer end of a ship's bowsprit. In the British navy the jack is nothing more than a small union flag, composed of the intersection of the red and white crosses; but in merchant-ships this union is bordered with a red field. See the article UNION.
JACK is used also for a horse or wooden frame to saw timber upon; for an instrument to pull off a pair of boots; for a great leathern pitcher to carry drink in; for a small bowl that serves as a mark at the exercise of bowling; and for a young pike.