Aba Transit Number
A number on a check, part of a code developed and used by the American Bankers Association. The transit number is used to aid the banks when clearing the checks, by signifying the financial institution as well as the Federal Reserve Bank used by that institution. This number is found near the upper right corner, and appears in the form of a fraction with a numerator and denominator. The numerator indicates the region where the bank is located, as well as the branch number. The denominator consists of the first four numbers of the routing number found at the bottom left of the check.