Quick Answer: In probability theory, odds provide a measure of the probability of a particular outcome. Odds are commonly used in gambling and statistics. For example for an event that is 40% probable, one could say that the odds are "2 in 5", "2 to 3 in favor", "2 to 3 on", or "3 to 2 against". In gambling, odds are often given as the ratio of the possible net profit to the possible net loss. However in many situations, the possible loss is paid up front and, if the gambler wins, the net win plus the stake is returned. So wagering 2 at "3 to 2", pays out 3 + 2 = 5, which is called "5 for 2". When Moneyline odds are quoted as a positive number +X, it means that a wager pays X to 100. When Moneyline odds are quoted as a negative number −X, it means that a wager pays 100 to X. Odds have a simple relationship with probability. When probability is expressed as a number between 0 and 1, the relationships between probability p and odds are as follows.