An amount set aside as reserve for bad debts. In general, companies make an estimate of bad debt expenses that might be incurred in the current time period based on past records as part of the process of estimating earnings. Most companies keep a bad debt reserve in the expectation that some small percentage of their creditors will not pay them in full. If the bad debt reserve is accurately estimated, then a company's net income will not be reduced when the debts are actually written off as being uncollectable.