A dead draw or dead card is an informal game term. A dead draw is a card that doesn't do anything for you, especially if it can't be played. Drawing Aragorn’s Bow (1R90) when Aragorn has died is a dead draw. Drawing Too Great and Terrible (3R85) when your opponent isn't playing Gandalf is a dead draw. Dead draws are an inherent risk of any card that needs to be played on another card, hate cards that punish particular enemy strategies, or any card that needs to spot or exert another card to function.
Some dead draws don't do anything useful, but can still be played to cycle your hand. Clever Hobbits (7U54) can be played even to discard zero Gollum conditions, even if Smeagol isn't in play. That doesn't do anything except generate two Twilight for your opponent, but at least you're getting the card out of your hand so you draw a new card next time you reconcile.