Value is considered to be the bet by which possible, risking less money to win more money. The value of the bets does not depend on the probability of the outcome, but of put up its prices.
The probability of passage valuable bet (value) may be equal to 10%, but if the odds with which it is possible to put on it, reflects a probability of 5%, this means that the bet is valuable (value). It is obvious that the bet in the example above would rather lose than win, but the point is that if you put 10 bets, one of them will play. Since the odds on it was equal 20, the player will be in the plus.
Search for valuable bets
To search for valuable bets players use the sites with comparison of lines among betting offices or scanners of arbitrage bettings. More advanced players create programs that differently (presumably better than the bookies) estimate the probability of events. Such players are called quants. How bookmakers treat valuable bets.
A valuable bet is a mistake of the bookmaker. Accordingly in fundamental betting office, the highs will be lower for the player. In the low-margin office or on the exchange rates there are no restrictions , but the fact is that to find a value on these sites is almost impossible.