The Data Universal Numbering System, abbreviated as DUNS or D-U-N-S, is a proprietary system developed and managed by Dun & Bradstreet that assigns a unique numeric identifier, referred to as a “DUNS number” to a single business entity. It was introduced in 1963 to support D&B’s credit reporting practice.
You can get it free for your US company here https://www.dnb.com/duns-number/get-a-duns.html
For Net Terms application from the supplier, consider avoiding it and tell the supplier you’ll pay by company credit card. This will save time and processing your application and avoid the hassle of reference verification.