I know there is a specific def ie: 10x10 with #50 is a volume of #5000.
As far as volume and work capacity, it would vary for me from exercise to exercise and be relative to gains.
I find 5x5 with say 80%-85% 1 RM in squat some good volume, but for curls, maybe not so much. However, I am also of the school that if you use the big compound exercises like squats, deads, rows, OHP's BP's etc. etc. you do not need a whole lot of volume on the small arm stuff say, since you are already pretty well trained using the big stuff.
Also, volume can be quite high, but intensity can be low, 10x10 with #100 pounds is #10,000 of work, 5x5 with #300 is #7500. The 10 sets of 10 has more volume less intensity but IMO the 5x5 will do quite a bit more to build you up and strengthen your entire body.
At a certain point volume, for the shear point of using volume, gets to be more aerobic (oxygen using) than anaerobic more tissue building. There is a line not ot cross IMO.
