Omaha is a poker game that was derived from Texas Holdem and the rules are identical, with the following two exceptions:
You are dealt four private cards in Omaha, whereas in Texas Holdem each player receives two.
You must use two cards from your hand in combination with three from the communal board cards to form a five-card poker hand.
This second rule gets new Omaha players into trouble, and Texas Holdem players must exercise caution in evaluating their hand as they make the jump to Omaha.
In Omaha your four private cards can be combined to make six unique two-card starting hand combinations. Texas Holdem players only have one two-card combination, so big hands are a lot more likely in Omaha.
In Omaha, players form the best five-card poker hand from a combination of nine cards: four in their hand and five on the board.
In Omaha, any hand that is possible given the configuration of board cards is also quite probable. That’s not the case in Texas Holdem.