Mastering is basically one of audio's a 'Dark Arts' especially if you have no idea about this essential audio discipline, because, even in the music industry there a still a good number of folk who still view Mastering as just that. A bit of a Dark Art.
If we were to make a filmy reference then Grading and or Colour Correction in the post production stage of a film may work. The idea being Grading the film is to make all your separate shots from your different reels of film come together in a coherent and cohesive whole.
The same can be said for Mastering. You bring all your musical elements together and after the audio had been mixed you Master with the object of bringing all your audio elements together in a coherent and cohesive whole. Savvi?
So audio Mastering is as dark an art as Colour Grading or a Telecine!