[1] Presence is similar to ambience, but is distinguished by a lack of explicit background noise.
Every location has a distinct presence created by the position of the microphone in relation to the space boundaries.
This is because of the unique spatial relationship between the microphone and boundaries such as walls, ceilings, and floors, and other objects in a room.
For this reason presence is normally recorded—like dialogue—in mono, with the microphone in the same position and orientation as the original dialogue recording.
[3] In the sound edit, presence occupies the same track as the dialogue to which it applies.