The K-system by mastering engineer Bob Katz is used in the film industry to put the focus on the dynamic range, instead of the loudness. K-System helps produce more consistent mixes and masters.
A lot of music is made in home studios, so people sometimes aren’t aware of the established practices these “big studios” implement. The K-System helps promote good mixing/mastering/monitoring practices. It is a great tool for a better and more consistent mix. Since no matter how carefully you mix or master a song, every listener will hear it differently.
Read more about this here: https://www.sweetwater.com/insync/mix-right-volume-level/