TAN is a unique number which is allotted to the persons or company who are responsible for deduction or collection of tax at source.
Some times assessee obtain TAN number to make some TDS payments. After those transactions and payments, and no need of that TAN in future or an assessee may have been allotted multiple TAN or assessee has closed down the business. In any of the condition, the assessee can surrender to the TAN number by mare making an application to the jurisdictional AO for cancellation.