What is it called when things become mute in a movie?

I've noticed in a lot of movies that there are points in time where the sound goes completely mute or sounds become distant. Sometimes there is music playing in the background, but that is absolutely all you can hear. It's usually a really dramatic part in the movie. Sometimes it's depressing or sometimes it has a pleasant mood. My questions are

-What is it called when it goes mute?

-What is it called when it plays only music?

-Who first introduced this style?What is it called when things become mute in a movie?
Essentially it's taking away diegetic sound (in universe sound) and replacing it with non-diegetic sound (sound from a source outside the universe of the movie). Hope that helps.