Diegetic Vs. Non Diegetic

When recording sound for films, there are two main types, those being diegetic and Non-Diegetic. Diegetic sound is sound that's visible or implied in the movie. Something like rain falling on the main characters hat or two characters talking to each other would be an example of shown diegetic sound. Non-diegetic sound is when the source of the sound isn't present or implied in the films universe, such as the music or a narration on a film. These two types of sound help build the world of the film for the viewers.