A bank account number is a unique identifier assigned to an individual's or business's account at a financial institution. This number is used to facilitate transactions, such as deposits and withdrawals, ensuring that funds are accurately credited or debited from the correct account. Typically, a bank account number consists of a series of digits, which can vary in length depending on the bank and the country. It is important to keep this number secure, as it can be used for unauthorized access to the account if it falls into the wrong hands.