Odds are probably the most important numbers to understand in sports betting since they indicate how much money a bet can win and how likely an outcome is. Historically several systems of quoting odds have developed in different parts of the world. The three most prominent of them are fractional, decimal, and moneyline or American odds.

A bookmaker (also known as a bookie) is a person or organization that accepts bets on a particular outcome of a sports event and pays to the bettors if their prediction turns out to be true.

The amount of money that is paid to punters if they are able to predict the actual outcome of an event is determined by odds. The higher the odds, the more money can potentially be won by the bettor. Unfortunately, outcomes that have high odds are very unlikely to happen; bookies have to make money somehow.