Omaha is similar to Texas Holdem in using a three-card flop on the board, a fourth boardcard, and then a fifth boardcard. Each player is dealt four holecards (instead of two) at the start. In order to make a hand, a player must use precisely two holecards with three boardcards. The betting is the same as in Texas Holdem, using a preflop, flop, turn, and river betting rounds. At the showdown, the entire four-card hand should be shown to receive the pot.
Roberts Rules of Poker