A stake is the amount of money that a punter has wagered on a racehorse. And a bettor’s winnings are calculated according to the horse’s odds. Bookmakers assign odds which attempt to approximate a runner’s chances of winning a race.
There are certain terms that are unique to horse racing. Ante post betting means wagering in advance of the race itself. A bettor can have a double when he has a bet on two different races, and the winnings from the first race can be rolled over to the second race. Trebles are bets on three races and bets on four or more races are accumulators. While it is difficult to generate a winning streak, a small wager can pay out huge dividends if successful.
A nap refers to a tipster's main bet selection at a given meeting. A starting price is an official price of a horse at which bets are settled in betting shops. Additionally, tote betting is when all money bet on horses in a race goes into a pool of funds. After the race, this pool is shared out amongst all those who have placed winning bets.
Odds against (i.e., 2/1, 7/1, 15/2, etc.) takes place when your horse's perceived chance of winning the race is less than 50/50. If your horse wins, you will receive your stake back plus your stake multiplied by the odds against it. For instance, you stake £10. If your horse wins at 2/1, you will receive: your £10 back plus your stake multiplied by the odds (£10 x 2) or £30 in total.
Even money is when your horse's perceived chance of winning the race is 50/50. If your horse wins, your stake will double in amount. Odds on (i.e., 1/2, 4/7, 3/10, etc.) is when your horse's perceived chance of winning the race is more than 50/50. If your horse wins, you will receive your stake back plus your stake multiplied by the odds on it. Because these wagers pose less risk for the punter, the returns are lower than ‘odds against’ bets.
Instead of a horse's odds being expressed as a fraction, bookmakers often regard odds as 'long' or 'short'. Odds that are said to be long (e.g. 50/1) point to the fact that a horse is very unlikely to win the race. Short odds (e.g. 2/1) indicate that a horse has a good chance of winning.