A 100% deposit bonus is a promotional offer commonly used by online casinos and sportsbooks to attract new players. When a user makes their first deposit, the platform matches the amount, effectively doubling the player's initial funds. For example, if a player deposits $100, they receive an additional $100 in bonus funds, allowing them to explore more games or place larger bets. However, it's essential to read the terms and conditions, as these bonuses often come with wagering requirements that must be met before any winnings can be withdrawn.