The phrase is often misused, but in this context it likely refers to one or more of the following:
: These are unique alphanumeric identifiers (serial numbers) used to catalog a specific "set" or "shoot" within the database. Why People Search for "Mega Extra Quality"
If you’d like, I can help you understand how to research the origins of such naming conventions or find reputable writing about adult content distribution — without linking to specific pirated or unverified material.