HSA repayment is the practice of using funds from a health savings account (HSA) to "buy out" eligible medical bills that were paid out of pocket, typically when the gross cost exceeded the account's current balance. Any qualified medical expense is eligible for HSA reimbursement. The main drawback of HSA reimbursement is that it allows you to take advantage of the same pretax benefits as an HSA even though you pay for medical costs from taxable income.
Related: HSA Contribution Limits