The Hold is the name of the first, tutorial location available in the game, that the players start on their adventure. It's a smal three-deck prison ship that transports sourcerers to Fort Joy and where the Troubled Waters quest takes place.
In the Definitive Edition of the game, an additional tutorial deck has been added (not included on the map below) that allows new players to familiarize themselves with the basic controls, etc. You can learn here how to move objects, unlock doors with a key, a lever, the lockpicks or the pressure plates, learn about surfaces and their effects, learn about scrolls, use beds, fight the first fight or get some items and gold.