You are understandably confused, since the terminology has migrated in usage to the point of incorrectness. The word, "mastering," means making the disc-shaped object which will directly be used in the creation of parts for pressing copies. The lacquer master and the glass master are such discs. The CD-R, DDPi, or .zip of Cue Wavs are premasters.
The process of processing the audio signals that go on a master is called, mastering, only when cutting grooves into a lacquer master disc and using the eq or limiting or whatever in real time as the disc is cut. If the lacquer master program is prepared in an earlier session - even by the same chick - this, too, would be premastering. By the way, to make a quadrophonic master, the clerk would want to use 16 channels of the identical EQ and limiters, since she would need one for each channel, times 2, for the preview path, and, times 2, again, for A and B switching (during banding). Even a stereo monogroove signal should be mastered with 8 channels of eq and such, unless a manually adjusted feed is used, and/or Global EQ settings. The "hit" to the lacquer cutting studio's acoustic footprint that is presented by an 8-channel console is enough to warrant considering doing premastering, even for lacquer. Compatibility processing can be applied in a more svelte setup.
Finally, since the glass master is used to make the parts for compact disc manufacture, the session before it, which is the one where these guys used their Foote compressors and their Inward Connections EQ, etc..., therefore, is called premastering. In premastering, anything goes. Ok. If making CD, you must put at least 4 seconds between tracks - even if the song is 3 seconds long. You must not exceed 79 minutes program. Etc... Artistically, you are free to explore... But to do it well, you would probably do as little as possible to make the song sound the way you can tell that it's trying to
, in the luxury of a revealing sound stage. Then again, if the mix is really sketchy, you might have to do quite a lot - provided no remix would be available...
Mastering, on the other hand, has a lot of requirements that are not subject to opinion. Is there just too much out of phase low frequency content to cut at 0 ref and not risk liftout of the pickup? Does the record have cutover grooves? Did the starting groove and lead-in happen well enough inside the outer diameter to leave room for holding with tongs (during metal mastering), but far enough towards the outer edge to allow an automatic tone arm deployer to drop the repro stylus in the correct spot (on the pressing)? Is the radius of curvature of the highest recorded frequency small enough that, at its recorded level, it risks that a playback stylus on a bent tone arm might skate across? Does the tracing distortion become objectionable by song 4? etc... Yes, there are real guidelines for this and a little bit of "wiggle room."
For premastering, it's all opinion, man. Apparently, there is a good amount of consensus over what sounds really good, so, stay thirsty, my friend.