Individual Taxpayer Identification Number
An Individual Taxpayer Identification Number (ITIN) is a United States tax processing number issued by the Internal Revenue Service (IRS). ITINs are issued by the IRS to individuals who do not have and are not eligible to obtain a valid U.S. Social Security Number (SSN), but who are required by law to file a U.S. Individual Income Tax Return.
Source: Wikipedia — Individual Taxpayer Identification Number (CC BY-SA 4.0)