On a price screen, "betting odds definition" comes down to two numbers. Betting odds are a price and a forecast in one number. A short explanation covers most of it: the odds say how much a winning stake returns, and they hint at how likely the book thinks the outcome is. What does not show on the surface is the margin, which is why reading odds well means looking past the payout to the chance behind the price.
A working definition of betting odds: the ratio between what a bet returns and what it risks, set by the book before the event. How odds work in betting follows from that. Short odds mean a likely outcome and a small return, long odds mean an unlikely one and a large return. What betting odds mean for a bettor is a trade: more potential payout always comes with less chance of collecting it, and the book's cut sits inside both sides of that trade.
The same numbers read differently by sport. In horse racing, betting odds work across a large field, so each runner carries a long price and the chances across the field add up well past one hundred per cent. In soccer, a match has three outcomes, home, draw and away, and the draw takes a share of the probability. A moneyline in sports with no draw simply names a winner, with a favourite at short odds and an underdog at long ones.
To interpret betting odds, turn the price into two numbers: the payout and the implied chance. At decimal odds of 3.00 a stake of ten returns thirty, so the betting odds payout is thirty with twenty of it profit. The implied chance is one in three. If the event happens more often than that over many tries, the price is generous; if less often, the price is short. Every other reading of a price rests on those two numbers.
Multiply the stake by the price: at 3.00 a stake of ten returns thirty, twenty of which is profit.
Divide one by the decimal odds, so a price of 3.00 carries an implied chance of one in three.
An odds table lines up formats side by side with implied chances, showing for instance that 1.50 means about sixty seven per cent and 11.00 about nine.
A race has many runners, so each carries a long price, and the chances across the whole field add up well past one hundred per cent.
A match can end in a home win, a draw or an away win, and the draw takes its own share of the probability.