There are 3 names in this directory beginning with the letter T.
TCS or Tax Collected at Source is income tax collected by seller in India from payer on sale of certain items.
Tax Deducted at Source is a method of collecting income tax. An organization/authorized person deducts tax on services they hire. They pay this tax on behalf of those service providers (who will in turn get credit on income tax). For tax deducted at source, the tax has to be recorded and tracked under the GSTR-7 (this return has to be filed by you monthly).
TRN stands for Temporary Reference Number. You can login using the TRN. After clicking on the REGISTER NOW link on the website, you can opt for the TRN option and enter the number. You will get a One-Time Password (OTP). Proceed after entering the number. You can check the status of your application under the Status column.