The ATT&CK framework, developed by MITRE Corp., has been around for five years and is a living, growing document of threat tactics and techniques that have been observed from millions of attacks on enterprise networks. The funky acronym stands for Adversarial Tactics, Techniques, and Common Knowledge. It began as an internal project and morphed into this behemoth of a public knowledge base that numerous security vendors and consultants have picked up.
The goal of the MITRE researchers is to break down and classify attacks in a consistent and clear manner that can make it easier to compare and contrast them to find how the attacker exploited your networks and endpoints and penetrated your network.
MITRE ATT&CK FAQ