Omaha poker is a type of Hold'em Poker that is popular in recent poker world.
To be different than Texas Hold'em ,it uses 2 out of the 4 cards in hand and 3 out of 5 hands on the public board.
The rank of a hands is same as for Stud Poker. (Straight Flush >Quads>Full house>Flush>Straight>Trips>Two Pair>Single Pair>High Card)
For more details about Omaha poker, please check below link:
Omaha Hold'em