TAN is a unique identification number which is allotted to persons who are deducting or collecting tax at source (TDS) on behalf of the Income Tax Department. For example:
Employers who deduct TDS on salary payments to employees,
Companies/ LLPs who deduct TDS on professional payments made to individuals and other entities,
Individuals who deduct TDS on payments made to NRIs.
Whereas PAN is a unique number allotted to a taxpayer like individuals, companies, etc. for their own direct tax liabilities.