secureboot is a part of the uefi firmware, when enabled, it only lets stuff run that’s signed by a cert in db, and whose hash is not in dbx (revoked). As you probably also know, there are devices where secure boot can NOT be disabled by the user (Windows RT, HoloLens, Windows Phone, maybe Surface Hub, and maybe some IoTCore devices if such things actually exist — not talking about the boards themselves which are not locked down at all by default, but end devices sold that may have secureboot locked on). But in some cases, the “shape” of secure boot needs to change a bit. For example in development, engineering, refurbishment, running flightsigned stuff (as of win10) etc. How to do that, with devices where secure boot is locked on?
This kind of golden key is what the FBI is pushing for. Now the cat is out of the bag, we can’t put it back in, though.