The term 'lay down cards' is a phrase used in the card game MELD. MELD is a game where players attempt to form combinations of cards, such as three or four of a kind, or sequences of the same suit. The goal of the game is to be the first player to lay down all their cards. To do this, players must lay down cards that form valid melds. When a player has no more cards left in their hand, they have successfully laid down all their cards and won the game.