Double down is one of dozens of poker variations you'll find in most online casinos. The rules of the game are quite simple, provided you understand the hand rankings of ordinary poker. Each player places a wager and is then dealt a single card. Once that card is received, he or she has the option of "doubling down," or increasing the bet two-fold.

In addition to the card dealt, there are four table cards, three of which are dealt face up. At this point, if the player wishes to Double Down, the dealer is obligated to match the bet. This simply means that the dealer (the casino) is responsible for covering the gambler's win. If the player wants to stay with his or her original stake, that's fine as well.

Scoring Double Down
Obviously, the fourth table card--the one dealt face down--has a lot of bearing on the outcome. Once that card is revealed, each player is rewarded based on the strength of his or her five total cards. While double down tables differ from casino to casino, usually only high pairs warrant some form of return, even if it's only even money.

If, on the other hand, a player manages a straight, a flush, a full house, or higher, these hands are paid out handsomely. The dealer must pay each player separately, as the hands are each considered independently of one another. Thus, while it's possible that the casino will face one large single payout, it's rare for the house to lose several hands at once as it frequently does in twenty one.