Bonus codes are unique combinations of letters and numbers that you can use at an online casino to unlock special bonuses and promotions. By entering in these unique bonus codes, players can take advantage of special offers like receiving extra cash, free spins, or increased loyalty points. Depending on the casino, the bonus code may provide a one-time or recurring promotion, and it is important to familiarize yourself with the terms and conditions associated with each bonus code in order to maximize your winnings.