Final answer:
Non-diegetic sounds are those heard by the audience but not the characters in a film, such as the musical score and voiceovers.
Step-by-step explanation:
The type of sound in movies that is heard by the audience but not by the characters is known as non-diegetic sound. These sounds are added to the film's soundtrack to enhance the viewing experience and can include elements such as the film's score, voiceovers, or sound effects intended to convey emotional responses or underscore dramatic moments. Conversely, diegetic sounds are those that originate from within the film's world, such as characters speaking, sounds made by objects in the story, or music coming from instruments within the scene.