A deck has several different meanings:

1. The floor of a ship or boat, especially the flat surface you walk on. Sailors work on deck, and passengers might stand on deck to watch the ocean. Ships often have multiple decks stacked on top of each other, like floors in a building. The upper deck gets fresh air and sunshine, while the lower decks are inside the ship's hull.
2. A wooden platform attached to a house, usually in the backyard. Families gather on the deck for meals outdoors or to relax in warm weather. Unlike a patio made of concrete or stone, a deck is built from wooden boards, usually raised off the ground.
3. A pack of playing cards. When you shuffle a deck of cards, you're mixing up all 52 cards before dealing them. Card players talk about cutting the deck or drawing from the top of the deck. People also use deck for other sets of cards, like tarot decks or flashcard decks.
4. A skateboard's flat board, where your feet stand. Skateboarders choose decks based on width, length, and the curve at each end.

The phrase all hands on deck means everyone needs to help immediately, borrowed from sailing when the entire crew had to come up on deck during emergencies.