Omaha is a variant of Hold'Em games in which players are dealt four hole cards that they can mix with five community cards to make their best five-card hand. Omaha is very particular: players must use exactly two cards from their hand plus exactly three cards from the board to make their best five-card hand. This can take a while to wrap your head around, but after a little bit of practice, you'll be able to see what hands you can make.
Because Omaha has a lot of hole cards that can mix with the board in lots of combinations, it's a popular game for math-minded players who can calculate odds of many different kinds of draws hitting.
Want even more draws? Omaha High/Low is a hugely popular variant, in which players can make the best high hand and the best low hand: the best high hand takes one half, and the best low hand takes the other.
As a result of Omaha's popularity, as well as the popularity of High/Low, many poker rooms offer Omaha tables, Omaha High/Low tables, and the two games make up the O (Omaha) and E (Omaha High/Low, also called Omaha Eights-or-Better) in HORSE.
Like Texas Hold'Em, Omaha is a blinds game: before any cards are dealt, the small blind is posted by the player to the left of the dealer (half the minimum bet) and the next player posts the big blind (the minimum bet). Antes might be used late in tournaments to force action.
Also like Texas Hold'Em, players can choose any betting structure they like when playing Omaha: limit, no-limit, and pot-limit. But unlike Texas Hold'Em, Omaha is more popularly played pot-limit rather than no-limit.
Players post their blinds. The dealer deals four hole cards. In the first round of betting (pre-flop), the action begins with the player to the left of the big blind: call, raise or fold. The action moves to that player's left. After the dealer acts, the action comes back around to the small blind, who can call, raise, or fold. If the blinds haven't been raised, the big blind can check (remember, never fold if checking is an option!) or they can call, raise, or fold
Three cards are dealt face up (the flop). Another round of betting, followed by another card dealt face up (the turn). Another round of betting, followed by the fifth card dealt face up (the river). A final round of betting.
If someone bets and no one calls, the bettor wins the pot. If someone bets and gets called, they show their hand, and players to their left either show their hand or mucks, the best five-card hand wins the pot. If no one bets on the last round, the first player to the left of the dealer shows their hand, and players to their left either show or muck.
Remember, Omaha uses the best five-card hand made from exactly two hole cards and exactly three board cards. In other words, having four of a kind in the hole is actually bad, you only play two of them as a pair!
See below to determine how to award the pot if playing Omaha High/Low.
Omaha High/Low gives players the chance to make the best high hand or the best low hand, with either taking half the pot.
A player can make a high hand and a straight hand to try to win both halves of the pot. So a player can use two cards from their hand to make a Full House with the board, and then two other cards to make a low hand.
If two players have the same high or the same low, they split the half of the pot that hand wins. So, if two players both have an A-to-5 straight, they each get one quarter of the low, but another player might win the high because they have a flush. This is sometimes getting quartered, usually, if a player loses one half of the pot and then splits the other, but it can get very crazy very fast if there are a lot of players with the nut low and one player taking the high!