Definition of outdraw
When one poker player outdraws another, it means that he hits a card that gives him the best hand when he was clearly not the favorite to win the hand. If two players are all in on the flop, one with 77 and the other with 88 on a 7-8-2 flop and the turn brings a 7, then the player with 77 is said to have outdrawn the player with 88. We could also call it a badbeat, suckout, one outer, etc.
Getting outdrawn, more common in Omaha than in Hold'em
In Hold'em, outdraws are more marginal. As in the example above, outdraws will occur 2% of the time, or 1 in 50 times, which is very low. In Omaha, outdraws will be much more frequent by the simple fact that each player has 4 cards instead of 2 and each new community card will energize the board in a new way. The difference in equity between hands is also lower in Omaha. If you take a Hold'em hand, a very good hand might have 82% preflop equity against a not so good hand, that's a huge equity difference. In Omaha, good equity differences are more like 60%/40%.