The term used for the sound that enhances the visual elements we observe is:

The term that refers to sound enhancing the visual elements we observe is actually "Soundtrack." This term encompasses all audio components that accompany visual media, including music, sound effects, and dialogue, contributing significantly to the emotional and narrative impact of the visuals. A well-crafted soundtrack can elevate the viewer's experience by reinforcing themes, creating atmosphere, and guiding emotional responses.

Ambient Sound typically refers to background sounds that establish the environment of a scene but are not the main focus of the audio. Natural Sound Source emphasizes raw or real sounds captured during filming, while Voice Over refers specifically to narration laid over a scene, often enhancing storytelling but not generally considered the broad spectrum of sound that enhances the visual experience like the soundtrack does. Understanding these distinctions helps clarify why Soundtrack is the most fitting answer in this context.