Everyone has an accurate idea of what the word "volume" is. To clarify, in music, it's usually considered to be the level of volume or force behind the music. In contrast to the general volume of an audio file, it is usually used in video files as an Audibles AAX file format.
They usually have several audio tracks. If they are stereo, there could be left and right tracks. In the case of videos, this could be a reference to various audio tracks that are in various languages. The tracks, naturally, could have a different volume. The overall volume can be adjusted in accordance with the preferences of media players, and the Track Volume can be determined within the file by the application that created the file.
Typically the volume can be set to either 100% or 0 percent, though variations could be observed.
When you check your video in search of hidden metadata and exif info, The Track Volume is typically connected to the track it is describing. At the minimum, it's an accurate reference to the tracks in some manner.