Fractional and decimal odds are two different ways of expressing the probability of a particular outcome in betting.
Fractional odds are commonly used in the UK and Ireland, and are expressed as a fraction (e.g. 2/1, 5/2, 3/4) or as odds (e.g. 2-to-1, 5-to-2, 3-to-4). They represent the ratio of the potential profit to the original stake. For example, if you bet £10 at 2/1 odds, you will win £20 if your bet is successful (plus your original stake of £10).
Decimal odds are more common in continental Europe, Australia, and Canada, and are expressed as a decimal number (e.g. 3.00, 2.50, 1.75). They represent the total amount that will be returned for every unit staked, including the original stake. For example, if you bet £10 at 3.00 odds, you will receive a total payout of £30 if your bet is successful (including your original stake of £10).
One advantage of decimal odds is that they are generally easier to understand and calculate than fractional odds. Decimal odds also make it easier to compare the relative value of different bets, as they show the exact payout for every unit staked.
However, fractional odds are still widely used in the UK and Ireland, and many experienced bettors prefer them because they are more familiar with the format and find it easier to compare odds across different bookmakers.