If you're reading this post, you probably know at least a little bit about the general game of poker: betting, hand rankings, reading a poker hand, the basics.
I'll address different levels of poker players to introduce them to the game. If the heading is too basic for you, skip to the next heading.
I know the game poker. What is Hold'em?
For you people unfamiliar with the game shown on many TV shows in the past decade, and the game commonly available to play free on social networking sites and many Internet and mobile platforms, I recommend searching on YouTube for a tutorial on the game; or if you prefer reading you can type into your search engine, "how to play texas holdem" or a similar search query.
When you've caught up with the rest of the audience, come back and read the next part.
I've played Hold'em. What is Omaha?
Omaha is a game closely related to Hold'em, played with four hole cards for each player. The community cards are similar to Hold'em, with a flop, a turn, and a river. One of the important distinctions is you always use exactly two of your hole cards and three of the community cards to determine your five-card hand.
The common variant of Omaha especially online is pot-limit Omaha high, abbreviated as PLO. Pot-limit means the biggest possible bet or raise on any action is limited to the size of the pot.
You can find videos and articles teaching Omaha poker by typing the query "how to play omaha poker" or a similar search into your favorite search engine.
I know the game Omaha. What is this high-low/8-or-better/O8?
High/low, Hi-Lo, split-pot games have been around for a long time and popular with many players. They combine a straight high form of poker with lowball poker in the same game.
Omaha 8 is played with the same "low hand" rules as Razz, a simple lowball poker variant, with the qualifier of eight-or-better meaning only low hands with a high card of 8 or lower can qualify to win the "Lo" half of the pot. When there is no qualifying low, the best high hand at showdown wins the entire pot.
When the hand goes to a showdown and at least one qualifying low hand exists, the pot is divided into the high and low halves, and any tied hands share the tied half of the pot.
The same person can win both the high and low. High and low hands are determined separately and can use the same or completely different hole cards and board cards. A player who wins both high and low without ties "scoops" the pot.
Because of ties, fractions of the pot can be won. A common occurrence is between two players with the same low hand and one winner for the high hand, so the winner of the high gets three-quarters (one-half for high and one-quarter for low), and the loser gets one quarter. The loser is "quartered" for the pot and may lose as much as half of the starting stack size.
With many players tied for one side of the pot, fractional pots can be awarded such as one-sixth or one-eighth of the total pot.
A quick overview of the "low hand" rules:
Aces are both high and low, and are considered the lowest rank as well as the highest. The best possible low or "nut low" always contains an ace either on the board or in someone's hand.
The best five-card low hand is A-2-3-4-5, which when read from high to low is 54321 and the only possible five-high low. It is also a straight. The ace-to-five low hand and straight is called "the wheel" and the five ranks it contains are "wheel cards" which can be represented by the letter W in hand descriptions.
The other three low ranks are 6, 7, and 8.
To compare two low hands, convert the hand to a five-digit number using the cards in sequence from highest to lowest, and then do basic math to find the lowest number, which is the best low hand.
For example:
Player Apu has the hand A-A-2-2
Player Boz has the hand 2-3-4-5
If the board on the river reads 5-7-8-K-K,
Apu's low hand is 87521
Boz's low hand is 87532
87521 < 87532
Apu wins with the low with the nut low.
Example 2:
Player Apu has A-A-2-2
Player Boz has 2-3-4-5
If the board on the river reads A-2-3-K-Q
Apu's hand is a set of aces with no low. The "worst" possible hand KQ321 is king high and can't qualify for low.
Boz has a wheel with 54321 and wins the low (and the high).