Breaking it Down: Diagetic V. Non-Diagetic Sound

Did you know that there is a distinction of music based on who hears it? Let me explain:

Diagetic Sound is music that both the audience and characters can here. Non-Diagetic sound is music that only the audience can hear.

A great example of Diagetic sound is the Red Circle Club Scene from the film John Wick.

https://www.youtube.com/watch?v=CTJlmlZWWHA