Low or short odds mean that the horse has a lot of money wagered on it to win (i.e., a favorite), while high or long odds mean less money has been wagered on it to win (i.e., a longshot). Although a professional will determine predicted “morning odds” before the race, the odds will continually change as bettors chance their money, and final odds or payouts will only be calculated after the finish of the race. Ultimately, favorites are generally considered to have a higher chance of winning, but longshots will have a higher payout if they win.
In 1949, R. M. Griffith first recorded a betting pattern now termed the “favorite-longshot bias,” which concludes that favorites are undervalued by bettors and longshots are overvalued. Although more overall money is wagered on favorites, the proportion of money wagered on longshots is consistently higher than expected. This pattern has been confirmed and replicated over the years, leading many researchers to conclude that bettors are attracted to risk. By backing longshots, they’re making wagers with low average returns and high variance, or many possible outcomes—they may gain a high payout, but it’s more likely that they’ll lose their money. As with many other types of gambling, bettors are thought to be drawn to the risk and uncertainty of these bets.
I used to dabble with online betting but the longest shot I ever went for (and I never bet on horse racing) was a 14/1 shot on Arsenal to beat Barcelona 2-1 when they were 1-0 at half time. 50p won me £7. The risk is too much for me but evidently not for so many. I blame Gamblor.