Sports Betting Terms Explained

Accumulator: A bet type, in which one attempts to predict the winner of two or more events; the decimal odds are multiplied together to arrive at a price, which will be paid, if the punter is successful predicting the winners of the events.
Arbitrage (Arb): A trading strategy, whereby one may take advantage of the movement of prices, the discrepancies in pricing, or the differences in prices, for guaranteed profits.
Asian Handicaps: Although fundamentally the same basic concept as the point spread, Asian handicaps are specific to soccer matches and provides an alternative to the standard win/draw/win scenario where if the handicap ends in a half point, a draw is not possible.
Betting Exchange: A new betting medium where you make your bets not with a bookmaker but with other punters online. You can choose to either back an outcome as you would normally with the bookmakers, you can play the role of the bookmaker and 'lay' an outcome or you can simply 'trade' the betting market.
Bookmakers' Margin: See 'Over-round'.
Even Money: A term used when an outcome is paying decimal odds of 2.0 (fractional odds of 1/1). Often referred to as 'yours for mine'.
Exchange Commission: The amount of money, paid by a winning punter to a betting exchange; a betting exchange earns its money by charging a percentage on winning wagers; generally, commission payable is based on a sliding scale from 2% to 5%, depending on the amount of money, which is either won or lost by a punter, over a period of time; the more that is either won or lost by a client, the lower will be the commission payable on winning wagers.
In-Running: Betting on an event which has already begun; to bet during an event.
In the Red: A betting term otherwise referred to as 'Odds On'. The profit to be made wagering on an outcome that is 'in the red' will be less then the stake. I.e. Decimal odds of 1.5; for every $100.00 that you invest you will receive $150.00 in return if your wager is successful. (Your original stake of $100.00 plus your $50.00 profit.)
Lapsed Bets: A previously unmatched bet, which a betting exchange has cancelled, due to the event commencing, and the betting market closing.
Lay: The opposite to back an outcome. To play the role of the bookmaker and oppose an outcome.
Lay-off: To bet on an opposite direction to either lock in profits or minimise a loss by either 'laying' the same outcome or, backing other outcomes in the same event.
Liquid Market: A betting exchange market, where there is a large number of bets being matched, leading to a competitive market, in which there is very little difference, between the back and the lay prices.
Long-term Market: A betting market, where the result of the betting event, will not be known for weeks, months or even years; to back a team to win a premiership at the beginning of a season; to back a player to be awarded the player of the season etc.
Matched Bet: A bet accepted by another punter on a betting exchange; matched bets cannot be cancelled, but a bet in the opposite direction would compensate for the original bet, effectively cancelling the initial transaction.
Money Line: Otherwise known as 'head-to-head' betting or a 'straight bet'. This is a bet type where you only have to pick the winner of an event. That is to say that you don't have to pick by how much a team will win or lose but simply who will win the game. The odds on each of the outcomes can be varied depending on the chances of the outcomes.
Odds Against: The opposite to odds on. An outcome is paying more than the initial stake. I.e. A runner paying greater then even money. (Decimal odds of 2.0)
Outcome: A betting result; the winner may be a player, horse, car, rider, driver, team, etc.
Over/Under Bets: Also known as totals. With this bet type, the bookmaker nominates a total of both teams' scores. Over/under bets can be offered on any sporting event and could be the total of sets, runs, points, goals etc. If the punter believes that the game will be a high scoring event, he may choose to bet the 'over'. For example, in an N.F.L. game, the posted total may be 38 ½ points. The punter will strike a bet with the bookmaker that the combined total of the two teams' scores will be greater than 38 ½ points. Conversely, another punter may believe that because of recent rain, the teams are going to find it very hard to score and as such may choose to bet the "under". I.e. He is betting that the total of the two teams' scores will be less than 38 ½ points.

These bets are also generally set at $1.90 for each of the outcomes.
Overlay: Otherwise know as an 'over'. A betting price, which is more than the price we believe it should be; a price representing a good value bet; for example, to obtain decimal odds of 3.0 on a horse, sporting event or special event, which one believes should be 2.0; to lay a bet also may constitute an overlay; to lay a horse or event at a price less than the price we believe it should be; such as, to lay a bet of 2.0, when the true price is believed to be 3.0. A subjective term.
Overround: Otherwise known as juice, edge, house edge or margin; the bookmaker's profit margin; converting the odds into probabilities (1/odds), and summing the probabilities, anything greater then one is the 'bookmaker's margin'. The greater the figure above 1, the greater the punter is disadvantaged.
Point Spread: Otherwise known as the betting line. With a point spread, the favourite is effectively given a total that for the bet to be successful, the team has to win by more than the allocated margin. In effect the underdog is given a number of point's head start. Let's look at an example.

The spread for a basketball game between two teams may look like the following.

The Boston Celtics +15 ½ $1.90
The LA Lakers -15 ½ $1.90

So the line in the above example is set at 15 ½ points. This means that the favourite has to win the game by 16 points and more for your bet to be successful, and the underdog can either win or lose the game as long as they don't lose by 16 points or more the bet will be successful. For example if the LA Lakers win by 15 points, you will have a losing wager.

In the extreme case of the reigning premier playing the bottom ranked team that posted their last win 2 years ago, the reigning premiers would indeed start at a very short price. This certainly has the effect of stifling the betting as there wouldn't be many punters which would be happy to risk $100.00 to make a profit of $5.00. Punters will invest their funds elsewhere which mean that if the bookmaker doesn't attract any turnover, they aren't making any money.

Usually the price will float around the $1.90 for each of the outcomes. Betting on the American sports has become so competitive that a number of large reputable bookmakers now offer prices of $1.93 for both outcomes. These odds can certainly move if the bookmaker doesn't take equal action on the two teams.

Note a draw is not possible if the point spread ends in half a point. One side will win the bet even if the game results in a draw if the point spread is not an integer.

The point spread evens the game up and induces more betting action on the event.