The [Advanced Access Content System (AACS)](wikipedia.org System) is a digital rights management standard developed by a consortium of media companies and technology manufacturers. It protects commercial Blu-ray and 4K Ultra HD discs from unauthorized copying. AACS operates using a layered system of cryptographic keys:

This creates a massive security risk for the average user. Clones of MakeMKV are rife with cryptocurrency miners and remote access trojans. The real MakeMKV is beta software that requires a constantly rotating "temporary activation key" (which the developer provides for free while it is in beta).

This is where comes in. It is a community-driven text file containing thousands of Volume Unique Keys. When you put a new disc in, MakeMKV checks:

Demystifying MakeMKV and AACS: How to Decrypt and Rip Blu-ray Discs

Disclaimer: This article is for educational purposes. Always ensure you are complying with the copyright laws of your country when ripping media.