Pari-mutuel betting is a form of gambling which involves betting on horse or greyhound racing. It is a widespread form of gambling. Wagering may take place through pari-mutuel pools, or bookies may take bets personally. Pari-mutuel wagers pay off at prices determined by support in the wagering pools, while bookies pay off at the odds offered at the time of accepting the bet. They may also pay off at the median odds offered by track bookies at the time the race started.