A DUNS number was a nine-digit identifier issued by Dun & Bradstreet, a private company, that the government required for federal registration before 2022. SAM.gov replaced it with the UEI, which it now assigns itself for free during registration, so you no longer need to get or maintain a DUNS number for anything federal. You may still run into old references to a DUNS number in legacy documents or older past performance records, but any new registration or lookup runs on the UEI instead.

In a sentence

"This past performance reference lists the contractor's DUNS number rather than a UEI." That is just a sign the document predates 2022; look up the same business by name in SAM.gov today and you will find its UEI instead.