Floating Jail, also known as a BRIG, is a type of prison ship used to detain prisoners. It is usually a large vessel that is moored in a harbor or at sea and is used to hold prisoners for extended periods of time. The term 'floating jail' is derived from the fact that the ship is not permanently moored and can be moved from one location to another. The use of floating jails has been documented since the 18th century and is still used today in some parts of the world.