ABA Routing Number This is a nine digit number that appears on all checks along with the bank account number. ABA actually stands for American Banker’s Association. It is also sometimes called the Transit Routing Number. The ABA number identifies which banks the account is from. Each bank is issues its own ABA number. When you send a bank wire or an ACH transaction from one bank to another, you need both the ABA number and the bank account number. ACH/Automated Clearing House