Noun
(gambling) A bet on some aspect of a game or competition that is not the main bet of the game or the prize of the competition; proposition bet.
(business) An investment or risk undertaken by a company that is not part of its core business.
(sociology) An investment of time, money, or resources that reinforces one's commitment to a course of action.
Source: en.wiktionary.orgA player wishing to wager on a side bet is usually required to place a wager on blackjack. Source: Internet
Fortune Pai Gow is another variation which allows players to make a side bet on a poker hand ranking of trips or better. Source: Internet
A non-controlling player of a blackjack hand is usually permitted to place a side bet regardless of whether the controlling player does so. Source: Internet
Blackjack games almost always provide a side bet called insurance, which may be played when dealer's upcard is an ace. Source: Internet
Pai Gow Mania was the first variation to be created which allows for two side bets instead of the traditional one side bet per hand. Source: Internet
Similar to fortune pai gow, is emperors challenge which also allows a side bet on a 7 card pai gow (no hand). Source: Internet