The likelihood of an outcome. In horse racing, it could mean the likelihood of a horse winning a race. In team sports, it’s the likelihood a team will win. The lower the odds, the more likely the outcome, and therefore the lower amount an individual better wins.
For example, 3-1 odds mean you will get three for every one that you bet. If you bet $10, you will win $30.
To calculate the probability of 3-1 odds, divide the denominator (1 here) by the numerator and denominator (3+1), and you get 1/4. So the probability of 3-1 odds is 25 percent.
Even money, also known as 50-50, or 1-1 odds, often is listed as "even" and means you have a 50-50 shot of winning. If you bet $1, you win $1.
Longshots, or higher odds, have less chance of winning but can have unintended consequences. Leicester City was listed as 5,000-1 odds of winning the English Premier League in 2015-16, and still did. British bookmakers lost more than 25 million euro ($28,438,975 in today's dollars) because of Leicester’s success.