A BSB (often referred to as "Bank State Branch") is a bank code used in association with the account number system used by each financial institution, it is a branch identifier used in Australia.
The BSB identifier is used for electronic transactions and processing of paper. It is a six number, the first two or three digits to indicate the "bank" and the other four digits to specify the "branch" of that financial institution. For example, the Australian BSB code "510-000" breaks down to: