Another hold 'em variant is Omaha hold'em. Each player is dealt four cards to his private hand instead of two. The betting rounds and layout of community cards is identical to Texas hold 'em. At showdown, each player's hand is the best five-card hand he can make from exactly three of the five cards on the board, plus exactly two of his own cards.

The most popular form of the game is high-low split, called many different names such as "Omaha Eight or better", "Omaha HiLo" or "Omaha8". Each player, using the above rules, makes a separate five-card high hand and five-card low hand, and the pot is split between the high and low (which may be the same player). To qualify for low, a player must be able to play an 8-7-6-5-4 or lower. A few casinos play with a 9-low qualifier instead, but this is rare.

http://www.gamblingweblog.com/2009/03/26/community-card-poker-omaha-h...