What does "swivel" mean?

Swivel: (Mil.) A small piece of ordnance, turning on a point or swivel; -- called also swivel gun. Wilhelm. Swivel bridge, a kind of drawbridge that turns round on a vertical axis; a swing bridge. -- Swivel hook, a hook connected with the iron strap of a pulley block by a swivel joint, for readily taking the turns out of a tackle. -- Swivel joint, a joint, the two pieces composing which turn round, with respect to each other, on a longitudinal pin or axis, as in a chain, to prevent twisting.