Sports betting arbitrage involves taking advantage of differences in bookmakers' odds in sporting markets. Arbitrageurs guarantee a profit from sports events by betting on every selection in the event to ensure a profit no matter who wins.
Arb players make guaranteed winning bets by finding the highest odds on each participant of a sporting event with different bookmakers. If the bookmakers' odds are all high enough it is possible to guarantee a percentage profit based on the total amount staked no matter what the outcome of the event.
Sports arbitrage opportunities are also referred to as "arbs", "surebets", "overbrokes" and "underrounds". These terms all mean exactly the same thing - "arbitrage opportunity".