A brig is a type of jail on a ship, especially a military vessel like a Navy warship. When a sailor breaks the rules at sea, they might be locked in the brig until the ship reaches port or until their punishment is decided. The word is also used more generally for a military jail.

On modern Navy ships, the brig is still the place where sailors who commit serious offenses are confined. It's different from regular jails on land because there's nowhere else to go: the ship is surrounded by ocean, so the brig keeps everyone in one place until proper authorities can handle the situation.

The word also refers to a specific kind of sailing ship with two masts and square sails. These brigs were popular in the 1700s and 1800s for trading and naval warfare. They were fast and maneuverable, making them useful for everything from merchant voyages to naval battles.