Matched betting is a method used to make guaranteed profit from bookmaker bonuses and incentives. There are hundreds of online bookmakers competing to get new customers to place bets with them. One way they do this is by offering incentives and promotions, such as a sign up bonus. For example, Coral will offer a £20 free bet if you place a £5 bet with our own money. Using simple matched betting methods and techniques, we will convert this into an easy ~£15 profit in less than fifteen minutes.
Here is the wikipedia article explaining what matched betting is all about: