Disk password

Link below regarding Firmware Password that Locks the Disk from loading anything

Set a firmware password on your Mac

Excerpt from above link

If you forgot your firmware password

If you can't remember your firmware password, schedule an in-person service appointment with an Apple Store or Apple Authorized Service Provider. Bring your Mac to the appointment, and bring your original receipt or invoice as proof of purchase.

Are you trying to log into macOS? Or are you trying to access an external drive (or some drive other than the internal drive)? Are you booting to the internal drive? Or as @P. Phillips mentions, are you trying to boot using special startup keys and encountering a padlock?

You definitely need to be more specific since as you can see there are multiple ways of interpreting "disk password".

You may want to review this article as well:

Writing an effective Apple Support Communities question - Apple Community