If your regular brakes should suddenly fail, then you will use what you have. For a short period of time the parking brake will be the emergency brake.
I can guess why the semantic games are played with the description of the “Reserve?” brake. If the regular brakes fail and the “Emergency” brake does a very poor job of stopping the vehicle, as would be expected, someone will smell money and will find a trial lawyer to sue a car maker for an inadequate “Emergency” brake. So there you have it, it’s a “Parking” brake.
The “Parking” brake actuates the rear wheel brakes, whether front or rear drive. I have never seen car with a parking brake that actuated the front brakes. Possibly a few may have had a parking brake as part of the transmission.