Betting is staking money (or some other form of value) on one's beliefs. It is considered rationally virtuous to bet on one's beliefs, as the real stakes force one to actually consider precisely what they anticipate will really happen. LessWrong has a culture of betting.
See also: Prediction Markets, Forecasting & Prediction, Forecasts (Specific Predictions)
The argument in favor of betting is that one should generally either accept a proposed bet, in order to make money in expectation, or update their beliefs so the bet becomes unprofitable. There are exceptions to this rule, some theoretical, such as the example of Omega and Omicron, and some practical, such as uncertainty about whether the bet will be fulfilled. Offering a bet forces someone to think more carefully and share their beliefs more precisely. Losing a bet, even small, can make it more emotionally visceral in a way that might lead to sharpening belief calibration more. Bets can be made about beliefs that can be immediately verified or about beliefs that will only be verifiable in the future....