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## Definitions for: O

### Odd

Synonims: Price, Probability.
Odd is a number that expresses the Probability of an event to occur. It also represents the profit of the Bet, therefore a bettor should look for the higher odds for a certain event in several bookmakers or Bet exchanges.
There are several ways to display the odds: Decimal odds, Fractional odds and american odds (also known also moneyline odds).

Decimal odds: Decimal odds are used in Europe (except in the United Kingdom). It’s the inverse of the probabilities of a certain event to happen.
Probability of the event = 1/ Decimal odd
Example: an event with 25% chances to happen has a decimal odd of 4.00 (= 1/0.25 ).
The Decimal odds value includes the Stake and the potential profit, so to calculate the total profit in that event it’s needed to subtract the Stake after multiplying the Stake by the decimal odd.
Profit = Stake * (decimal odd – 1)
Example: a Bet with 10 unit Stake at 4.00 decimal odd, has a profit of 30 units (= 10 * (4.00 – 1) ).

Fractional odds: it’s a way of representing the odds used in the United Kingdom. Display is shown as a fraction, where numerator represents amount to win from stakes shown in denominator.
Probability of the event = 1/ (fractional odd + 1)
Profit = Stake * fractional odd
Example: odds of 1/3 mean that bettor wins 1 unit for each 3 units staked (thus equal to 1.333... in decimal format).

American odds: Unlike previous two types, display depends on ratio between Stake and potential profit.
If potential profit is higher than Stake, american odds are positive, and show profit from Stake of 100 units.
If potential profit is lower than Stake, american odds are negative, and show Stake needed to gain profit of 100 units.
If potential profit is equal to Stake (Decimal odds 2.00, Fractional odds 1/1 (evens)), american odds may be displayed as +100 or -100.
In negative american odds: Profit = Stake * 100/ american odd
In positive american odds: Profit = Stake * american odd /100
Example: American odd of +150 and Stake of 100 => Profit = 100 * 150/100 = 150;
American odd of -150 and Stake of 100 => Profit = 100 * 100/150 = 66,67

Odds Convertion:
Convert Fractional odds to Decimal odds:
Decimal = Fractional +1
Convert American odds to Decimal odds:
In positive American odds: Decimal = 1 + (American / 100)
In negative American odds: Decimal = 1 + (100/ American)

### Outsider

Synonims: Dog, Underdog.

### Over/Under

Synonims: Overs, Unders.
A Bet on whether the total number of goals/points in a game will be over or under the stated number.

Over/Under Types Explained:

Over/Under 2 goals line – Under 2 goals selection wins if the match ends with less than 2 goals scored. Over 2 goals selection wins if the match ends with more than 2 goals scores. Bets in this Market are void and stakes are returned if the match ends with exactly 2 goals scored.
Over/Under 2.25 goals line – This is actually a Bet that consists of two bets: one Bet on Over/Under 2 goals line and one Bet on Over/Under 2.5 goals line. The amount you place on the total Bet is divided between the two types of bets. Under 2.25 goals selection wins if the match ends with 1 goal or less. If the match ends with 2 goals scored: Under 2.25 selection wins 50% and it’s returned the other 50% of the Stake; Over 2.25 selection loses 50% and it’s returned the other 50% of the Stake. Over 2.25 goals selection wins if the match ends with 3 goals or more.
Over/Under 2.5 goals line – Under 2.5 goals selection wins if the match ends with 2 goals or less. Over 2.5 goals selection wins if the match ends with 3 goals or more.
Over/Under 2.75 goals line – This is actually a Bet that consists of two bets: one Bet on Over/Under 2.5 goals line and one Bet on Over/Under 3 goals line. The amount you place on the total Bet is divided between the two types of bets. Under 2.75 goals selection wins if the match ends with 2 goal or less. If the match ends with 3 goals scored: Under 2.75 selection loses 50% and it’s returned the other 50% of the Stake; Over 2.75 selection wins 50% and it’s returned the other 50% of the Stake. Over 2.75 goals selection wins if the match ends with 4 goals or more.

### Overround

Synonims: Betting Book, Book Value.
Sum of probabilities of each runner to win the Market.
In theory, sum of probabilities of each runner to win is 100%. Odds derived from these probabilities are called fair odds or true odds.
However, bookmakers include their margin into fair odds before offering them to bettors, so sum of probabilities is always higher than 100% (usually around 110%).
Lower the overround, better the odds from bettor's perspective. If overround is lower than 100%, bettor can achieve guaranteed profit by backing all selections (Dutching), no matter what the outcome of the event will be, so a single Bookmaker will never allow overround below 100%. However, combining odds from several bookmakers, bettor can achieve overround below 100%, and that method of betting is known as Arbitrage.
On Betfair the overround is shown above the odds panel on the Back side. Betfair is a Bet Exchange so it charges his clients after the bets as a commission over the winnings. As that commission is not included in the odds, the overround in Bet Exchanges is lower than in Bookmakers.

### Overs

Synonims: Over/Under, Unders.