Definition of combodraw
A combodraw is a term used more often in Omaha than in Hold'em (although it is still used in Hold'em). The reason is that all-ins are more common in Omaha than in Hold'em. If, for example, two Omaha players face off on an A-8-9 flop with two spades and one has AAxx and the other has JTxx with two spades, we would say that there has been a "top set versus combo draw" all in. What we mean by combodraw is a multitude of turn and river combinations that can help the player with JTxx. In this case, all 7s, Qs and spades could give the player with a combodraw the best hand.
Combodraw and equity
Poker players value ready-made hands (like AAxx in the above example) very much. And they are right of course because they are very strong hands, but some combodraws are stronger than some ready-made hands. Let's take an example of Hold'em and an 8-9-A flop with two diamonds. One player has a ready-made hand with AK (top pair, top kicker) and the other player has a combodraw (JT in diamonds). If both players go all in on the flop, who will win the pot more often in the long run? The player with JT in diamonds will win the pot 56% of the time compared to 44% for his opponent!