A First Deposit Bonus in the UK is a promotional offer provided by online casinos and betting sites to attract new players. When users create an account and make their initial deposit, they receive a bonus, often in the form of extra funds or free spins. This incentive allows players to explore the platform and try out various games without risking too much of their own money. However, it's essential to read the terms and conditions, as these bonuses typically come with wagering requirements and other restrictions.