It's the same as in English (and Italian, and probably others). It refers to space, sound and things like "Vol. 1, Vol. 2 ..."
The male voice does not even come close to pronouncing this correctly.
It has to do with the way some of these exercises are set up. We're fixing them as we find them (I'm about to go locate this one, now), but there are a lot of them scattered throughout the tree.