This figure is used by a company's accounting staff in its monthly bank reconciliation, where the staff isolates all differences between the bank's and the company's records regarding a bank account through a bank reconciliation procedure, which may (and usually does) require some journal entries in the company's accounting records to record such items as interest income and service fees.
When a company engages in a daily bank reconciliation, the bank balance is the ending cash balance appearing on the bank's website for the relevant bank account for the preceding day. The accounting staff will then use this figure as part of its daily bank reconciliation procedure.
The ending date on a bank statement (and the corresponding bank balance) does not necessarily coincide with the last day of a month, since a company may request a different ending date for its bank statements.
The bank balance is also known as the balance per bank.