Matched deposit bonuses in Singapore's sports betting are offers where a betting site matches a percentage of your initial deposit with bonus funds. For example, if you deposit a certain amount, and the offer is a 100% matched deposit bonus, the betting site will provide the same amount as bonus funds, effectively doubling your bankroll. However, these bonuses usually come with terms and conditions like wagering requirements and time limits, so it's important to read the fine print before participating.