A CMR (Client Master Report) is a document issued by your Depository Participant (DP) that contains all the details of your demat account, such as your name, PAN number, bank details, DP ID, client ID, and the depository (NSDL/CDSL) with which your account is held.

It is important because it acts as a proof of ownership of your demat account and is often required when linking your demat account with trading platforms, banks, or brokers.