One of the most familiar features of a castle's defences: a ditch filled with water which surrounded the building. They were often stocked with fish, a source of fresh food in winter; perhaps also ducks and swans. (However, the *garderobe would have been directly over the moat.) A moat was also useful in offering a serious impediment to attackers wishing to mine beneath a castle's walls.
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.