A value added tax identification number or VAT identification number is an identifier used in many countries, including the countries of the European Union, for value added tax purposes. You can read about it here: VAT Identification Number
The Data Universal Numbering System, abbreviated as DUNS or D-U-N-S, is a proprietary system developed and regulated by D&B (https://www.dnbnumber.com) that assigns a unique numeric identifier, referred to as a "DUNS number" to a single business entity. For more information click here: DUNS Number