A draw is an incomplete hand that needs the help of additional cards in order to become a valuable holding. You will most likely have the winning combination if you hit your draw, but you will have a very weak holding if you miss it in most cases.
The most common draws in poker are a flush draw and a straight draw.
For example, let’s say you have a 3s2h, and the flop is 6h, 5c, Qs. In this case, you have an inside straight draw, and if you hit a 4, you will most likely have the best hand. In some cases, even if you have a draw, you might be drawing dead and have no outs to win the hand.