What's The Difference Between Diegetsic Or Non-Diegetic Sound?

What is the difference between diegetic and non-diegetic sources sound?
Diegetic sound is any sound presented as originating from a source within the film's world. Diegetic sound can be either on screen or off screen depending on whatever its source is within the frame or outside the frame. Non-diegetic sound is represented as coming from the a source outside story space. The distinction between diegetic or non-diegetic sound depends on our understanding of the conventions of film viewing and listening. We know of that certain sounds are represented as coming from the story world while others are represented as coming from outside the space of the story events. A play with diegetic and non-diegetic conventions can be used to create vagueness

horror, or to surprise the audience comedy.
Can the music in a movie be both diegetic and non-diegetic?
Either way, diegetic music is when the characters in the film can also listen to the same music as you the audience, like for example if one of the characters puts music while driving his car, he can hear the same music as Non-diegetic is when the character can't listen to the music, I mean it doesn't take place in the reality of the movie, example, a couple in the film is kissing and the audience can listen to a piece of classical music, it's obvious that the characters are not listening to that music in the reality of the film, only the audience can hear it.