Overdraft protection is a financial service offered by banks that helps customers avoid declined transactions when their account balance falls below zero. If a customer tries to make a purchase or withdraw money that exceeds their available balance, the bank will cover the difference, allowing the transaction to go through. This service can be linked to a savings account or a credit line, which means funds will be drawn from these sources to cover the overdraft. While it provides convenience, customers may incur fees or interest charges, so it's important to understand the terms associated with overdraft protection.