Ambient is an adjective used to describe an aspect of the environment that completely surrounds you, but in a mellow way, like ambient music played softly throughout a restaurant, or the ambient orange glow during a setting sun.
Ambient describes some pervasive quality of the surrounding environment, like the ambient lighting in a movie theater, or the ambient temperature of a room. Most times when you’re hearing silence, you’re hearing some ambient noises too, like the hum of a refrigerator or the whistle of a breeze. Usually ambient describes a quiet or peaceful quality, but it can be aggressive too, like the ambient drone of war planes flying above that you can hear no matter where you hide.