Sound
Layering
Also called depth, front-to-back depth
Layering is the sense of depth in a presentation: the impression that some instruments sit in front of others rather than all on one flat plane. It is the front-to-back part of soundstage.
Recordings made in a real acoustic carry depth cues in their reverberation. A product that preserves those cues lets the back row of an orchestra sound further away than the soloist; one that flattens them puts everything at the same distance.
Layering is often praised on Open-back headphones and well-placed speakers. Like Soundstage, it is an impression rather than a measurement, and listeners disagree about which products do it best.