Bad debt means a customer owes you money but you can't collect it. They have a debt with you, but you know you aren't going to get paid. If your business uses accrual method accounting, you can sometimes write off bad debt in QuickBooks as a deduction. When invoices you send in QuickBooks become uncollectible, you need to record them as a bad debt and write them off. https://www.businessaccountings.com/write-off-bad-debts-in-quickbooks/