In addition, most digital recorders let you cut and paist from the virtual tracks. Meaning - if the vocalist laid down the vocal part 8 times (on the 8 virtual tracks of track 2) you could cut the 1st verse from take 1, the chorus from take 2, the bridge from take 3, etc) and "compile them as the "master" on track 2.
Another use of the phase "virtual tracks" could refer to MIDI controlled tracks. As an example, if you sync a multi track to a drum machine and have the drum machine play "with the" multi track (without actually recording the drum sounds) - this would also be considered "virtual tracks". In the days before there were limitless digital tracks available, we use to delay "tracking drums" until last to preserve tracks. In fact it was common to record the drums drirect to the 2 track mix as a "virtual track".
However, history lesson aside - I think the definition you are looking for is what Green Hornet explained.