It is a more accurate verification of your account. When you first register, the account is considered a non-verified account and withdrawal limits are in place. 0.5BTC per day
It means "Know your customer" (KYC) and is used to verify the identity of our customers, in order to avoid: identity theft, financial fraud, money laundering, etc.
This process is necessary to increase the operating limits of money in your account. To send the necessary documents, go to Account / Account Verification, then upload them.