A Tax Identification Number (TIN) is a unique number assigned by the government to individuals or entities for the purpose of tax administration. It is used to identify taxpayers and track their financial transactions for tax purposes.

TINs come in different forms and are assigned based on the jurisdiction and type of taxpayer. For individuals, TINs are often referred to as Social Security Numbers (SSN) in the United States, National Insurance Numbers (NIN) in the United Kingdom, or Personal Identification Numbers (PIN) in some other countries. For businesses, TINs are often referred to as Employer Identification Numbers (EIN) in the United States.

TINs are required for many tax-related activities, such as filing tax returns, making tax payments, and claiming deductions. Employers are required to obtain TINs for their employees and to report their employee's earnings to the government using their TINs.

Having a TIN is important because it enables individuals and businesses to comply with their tax obligations and to participate in the tax system. Without a TIN, individuals and businesses may face penalties, fines, and other consequences for failing to file and pay taxes.