In sailing, a brig is a vessel with two masts at least one of which is square rigged.

In modern parlance, a brig is square rigged on both masts, and this is the standard name for such a vessel.

Previously, brig has been used as an abbreviation of brigantine, which in modern parlance is the standard name for a principally fore-and-aft two-masted rig with a square rigged foremast but which also has other historical meanings. See brigantine, brig sloop.

A brig is a jail on a United States Navy or Coast Guard vessel. The term is also sometimes used for any jail within a U.S. Military installation.