In horse racing, the starting price (SP) is the odds prevailing in the on-course fixed-odds betting market at the time a race begins. The method by which SPs are set for each runner varies in different countries but is generally by consensus of an appointed panel on the basis of their observations of the fluctuation in prices.
In the UK, the SP is an average of the prices offered by the on-course bookmakers at the start of each race. These prices form the basis of the pay out to winning punters if they haven't taken a specified price themselves, and are not known by the punters at the time of betting .
Some online bookmakers offer ‘best odds guaranteed’, meaning that if a punter takes an early price on a race and the SP turns out to be better (that is, higher), then if the punter wins, the payout is at the SP. This is aimed at removing hesitancy among punters prompted by fears of taking what might prove to be a poor (that is, low) price before the race.