A company Taxpayer Identification Number (or TIN) is a number assigned to your company for the purpose of administering the company taxes and VAT. It is most often allocated by the tax authorities within your country - as opposed to your company registration number, which is issued by the company registry office.

The actual word used to identify this number varies between countries. For example, in the EU it's referred to as a VAT number, while in the US it's an Employer Identification Number (EIN).

If you are unsure of what your company's taxpayer number is, please see the resources below.

Resources:

VAT numbers in the EU (information about VAT numbers for European Union members)

TIN / VAT number outside of the US (Wikipedia article covering TIN number)

TIN in the United States (IRS website)