A deposit bonus is a bonus amount credited to your account when you make a deposit to your account the amount of bonus would be determined by the amount you credit and the club you are depositing with, and their terms and conditions relating to any such amount.
Many online bingo clubs offer 100% bonus match on first deposit with varying deposit bonuses awarded for each subsequent deposit.
There will be a set limit to the amount you may first deposit usually up to two hundred pounds.
Bonus deposits will have attached to them certain conditions when it comes to withdrawing the funds and you will have a minimum wager amount to be played before any withdrawals can be processed, this will vary depending on the club concerned.

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Some clubs add the bonus as cash to your account where as others add it as bonus points or in a separate account available for play once you have used your deposit amount.
Again worth checking the details with the online bingo club or site you are registering with.