Person offering odds, usually a bookmaker. Exchanges allow punters to lay as well as place bets.
A lucky 15 consists of 15 bets involving four selections in different events; i.e. four singles, six doubles, four trebles, and one fourfold. Same as a yankee, plus four singles. The 'lucky' name arises from the bookmaker sometimes paying a bonus for all four correct selections, or only one correct selection.
A lucky 31 consists of 31 bets involving five selections in different events; i.e. five singles, 10 doubles, 10 trebles, five four-folds and one five-fold. Same as a canadian, plus five singles.
A lucky 63 consists of 63 bets involving six selections in different events; i.e. six singles, 15 doubles, 20 trebles, 15 four-folds, six five-folds and one six-fold. Same as a heinz, plus six singles.