A deck is a platform or a section of floor on a ship. If you're on a cruise with your family, you might tell your brother to meet you on the upper deck after lunch to play shuffleboard.
Most decks are open, without a roof, and positioned high on a ship . Typically, the bridge deck houses the ship's helm and navigational tools. The deck behind your house isn't much different from a ship's deck — it's a flat platform too. Other kinds of decks are a pack of cards, the board part of a skateboard, and the floor: "Hit the deck!" To deck a person is to hit them, but to deck your house is to decorate it.