Definition of wraparound
The term wraparound is mostly used in Omaha. When you have a good draw in Omaha, we say you have a wrap. But when you have a very strong draw that gives you more than 17 outs (an out is a card that can help your hand) we say you have a wraparound. For example, if you have 8s-9s-Kh-Qh over 2s-Ts-Jh, you have a wraparound. Here, all spades can help you (so you have the flush), all 7s will give you a straight, and all aces will give you a straight. You also have a backdoor flush draw with your two hearts in hand. Eights will also give you a straight as will kings.
How to play your wraparound?
Using the example above, we have no pairs, straights or flushes, but with the number of outs we have, we will have to play our hand aggressively. By playing a wraparound aggressively, we maximize our equity through folding equity. For example, if we check-raise on the flop higher, we encourage our opponent to fold. Every time he folds, he throws away equity that comes back to us. And by aggressively playing a wraparound, we can entice our opponent to push all in on the flop with worse draws.