A tax ID number is defined as an identification number used in implementing tax laws by the Internal Revenue Service, or IRS. The tax identification number is also referred to as TIN and is issued by either the IRS or Social Security Administration, or SSA.
There are multiple variations of a tax ID number. This includes Social Security numbers, employer identification numbers, individual taxpayer Identification numbers, taxpayer identification numbers for pending U.S. adoptions and preparer taxpayer identification numbers.
Tax Identification numbers are used on tax-related documents, including tax returns or statements. The number must be submitted when claiming treaty benefits.
For the individual, his Social Security number is used for his tax identification number.