Exercise volume typically refers to the amount of work completed in a workout and is calculated by multiplying sets x reps x weight.
Using this same idea you could zoom in and analyse your exercise volume per exercise or muscle group. Or zooming out you could analyse your weekly exercise volume.
If you find you are having a hard time recovering from your workouts then exercise volume is something you may need to look at dialling down. Conversely, if you are struggling to make any gains then your exercise volume may need dialling up.