Overround and Overbroke (general terms )

Adding up the probabilities as shown by the odds of all the participants in an event for a particular bookmaker gives a percentage. While mathematically the total probabilities of all participants in an event must be 100% (one participant - and only one - can win) bookmaker’s total percentages are set to add up to over 100% because it’s the amount over 100% that represents the bookmaker’s profit. A book with a total percentage over 100 is called overround. A book that adds up to less than 100% is called overbroke which means that a punter could back all the participants and know that the total of their lost stakes will be less than their winnings (a good, if rare, thing).