It is a generated passcode required to transfer an Internet domain name between domain registrars. Example: GoDaddy to Brixly or any other registrars out there. This provides an extra layer of security and protects against unauthorized transfers.
Depending on your current host, you can access or request for this through the settings.
Note: As there are multiple web hosting companies, they'll have different ways so you may need to contact their respective support team to assist you on how to do it.
Here's a video you can watch to know more about this process: