The TIN is the tax id number.  It is assigned by the IRS.  The formal SBA definition follows:

  The Taxpayer Identifying Number (TIN) was developed by the Internal Revenue Service (IRS) and is required by the Code of Federal Regulation. The TIN consists of two types of identifying numbers: social security numbers and employer identification numbers. For information on obtaining a TIN, call the IRS at (800) 829-1040. 


The DUNS number is assigned by Dun & Bradstreet who rate companies on their credit worthiness (usually called a D & B rating). Businesses are assigned a DUNS number and can be identified simply by using that number. The formal SBA definition follows: 

   The Data Universal Numbering System (DUNS) was developed by Dun and Bradstreet Corporation in 1962 to identify businesses in its automated files. There are approximately 11 million numbers issued to active domestic firms. For information on obtaining a DUNS number, call the Dun and Bradstreet offices at (800) 333-0505.


 
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