DEFINITION of 'Account Number'
The primary identifier for ownership of an account, whether a vendor account, a checking or brokerage account, or a loan account. An account number is used whether or not the identifier uses letters or numbers.
BREAKING DOWN 'Account Number'
At one time, it was common to use a Social Security number as the primary identifier, particularly for employees (for payroll or human-resources identification). Because of the proliferation of identity theft, however, this practice has been all but eradicated. It is not a good idea to use a Social Security number for any type of account, or as a user name or password for electronic identification.