Jacks meaning : A coarse mediaeval coat of defence, especially one made of leather. A man. A device or utensil. A non-tool object or thing. A plant or animal. The edible fruit of the Asian tree (Artocarpus heterophyllus); also the tree itself. A home run. (games) A children's game involving picking up objects; knucklebones; jackstones. Alternative form of jakes: an outhouse or lavatory.