Fixed odds betting is the most common form of betting. It is the action of placing a bet at pre-determined odds so that you know exactly how much you stand to earn should a bet be successful.
This protects you against fluctuation of odds and no matter what changes throughout the course of the bet, the return will be as the odds where stated when the bet was placed. This offers protection on odds and can be beneficial when odds are fluctuating, as a punter can benefit from peaks in betting without suffering should the odds shorten.
Although this is beneficial to punters, the bookmaker will always have the added benefit of selecting the odds so that profitability is gained on their part. There are further rules around fixed price betting on some sports such as horse racing where non-runners can occur, so it is worth checking with the individual bookmaker for any caveats.