The mastering process is crucial in today’s music market. It is quite like mixing, but doing it on the master track rather than on each instrument. The goal of mastering is to further polish the mix of the song, fix some imperfections, and sometimes optimise or change the whole listening of the song. Other than all of these, a general purpose for mastering is to make the loudness of the song meet the market standards. Loudness is measured by LUFS, it stands for loudness units full scale. The loudness units are the same as decibels, with one key difference: they attempt to factor in the ways in which our ear-brain system interprets loudness based on the tonal balance of a sound. As the development of artificial intelligence, mastrering is becoming more automated than before. You can now analyse your track using iZOTOPE’s Ozone and it will do the adjustments of value on eq compression and so on by itself. Although the results were not always satisfying but i think it stands for the future of mastering, where human are more relied on machines rather than ears, especially when you don’t want any creative process on mastering, you just want it to sound correct.
Reference: https://www.izotope.com/en/learn/what-are-lufs.html