NOTE: Not all facilities have a Dun & Bradstreet Number. If you do not have one, it is not required on your report and you can just enter "N/A" in the field.
(Source: https://fedgov.dnb.com/webform/pages/dunsnumber.jsp)
Created in 1962, the Data Universal Numbering System or D-U-N-S® Number is D&B's copyrighted, proprietary means of identifying business entities on a location-specific basis.
Assigned and maintained solely by D&B, this unique nine-digit identification number has been assigned to over 100 million businesses worldwide.
A D-U-N-S® Number remains with the company location to which it has been assigned even if it closes or goes out-of-business. The D-U-N-S® Number also "unlocks" a wealth of value-added data associated with that entity, including the business name, physical and mailing addresses, tradestyles ("doing business as"), principal names, financial, payment experiences,industry classifications (SICs and NAICS), socio-economic status,government data and more. The D-U-N-S® Number also links members of corporate family trees worldwide.
The D-U-N-S® Number is widely used by both commercial and federal entities and was adopted as the standard business identifier for federal electronic commerce in October 1994.
The D-U-N-S Number® was also incorporated into the Federal Acquisition Regulation (FAR) in April 1998 as the Federal Government's contractor identification code for all procurement-related activities.
(Source: http://www.dnb.com/duns-number.html)
Before you can bid on government proposals, you need to obtain a Dun & Bradstreet, or D-U-N-S, Number, a unique nine-digit identification number for each physical location of your business. When you apply for a DUNs Number with D&B, the Data Universal Numbering System issues a nine-digit number that is unique to your company. This DUNs number is used to create your business credit file, similar to how your social security number is used to identify your personal credit reports.