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Maiden
In flat racing, a maiden is a horse that has never won a flat race other than a national hunt flat race in Great Britain or Ireland. For steeplechases and hurdle races, a maiden is a horse which has never won a steeplechase or hurdle race in Great Britain or Ireland. For National Hunt flat races, a maiden is a horse which has never won a National Hunt flat race in Great Britain or Ireland.

Mare
A female horse five or more years old.

Money line
US term. This is a bet to predict who will win a football, basketball or ice hockey event outright, i.e., without a spread. If the final score is a tie (known as a push), the bet is considered void, and your stake is refunded.

Monkey
Slang for £500.