Below-decks is a nautical term used to describe the area located below the main deck of a ship. This area is generally used for storage and living quarters for the crew. While below-decks is the most common phrase used to describe this area, there are a number of synonyms that can also be used. These include the terms lower deck, lower hold, lower level, lower deckhouse, and sub-deck. These synonyms are often used interchangeably with below-decks, and all refer to the same part of a ship. If you're talking about life aboard a ship, it's good to know these different terms to add variety to your language.