Drawing thin in poker occurs when a player has very few outs by the river to make a winning hand. This is slightly better than drawing dead, as they still have some chance to draw the right card, albeit a very slim one.
Drawing Thin Poker Example:
Let’s say you have a 9c 8c hand, and your opponent has a Js Th hand. The turn brings Jc Tc Ts 5h to the board. Your opponent has a full house. You’re drawing thin and still have a chance, as you can still win if you make a straight flush by getting either the Qc or 7c.