In the (sports) betting community the noun wager usually is the amount of money that the gambler has put into the bet.
In the current (October 5, 2014) version on the word gambling at Wikipedia it is stated that:
Gambling is the wagering of money or something of material value (referred to as ”the stakes”) on an event with an uncertain outcome with the primary intent of winning additional money and/or material goods. Gambling thus requires three elements be present: consideration, chance and prize. The outcome of the wager is often immediate, such as a single roll of dice or a spin of a roulette wheel, but longer time frames are also common, allowing wagers on the outcome of a future sports contest or even an entire sports season.
Wagers are not only common in the betting community but also in the scientific world!
Wager is one of plenty of words/phrases/abbreviations in sports betting I have written about. See this dictionary for all the terms I have tried to explain.