Volume usually means total work—often approximated as sets × reps × weight for a muscle group or lift across the week. Intensity is how heavy or hard those reps are (percentage of max, or proximity to failure).
Raising both at once is a fast track to burnout. If intensity climbs, volume usually must dip slightly to stay recoverable. If you add sets or sessions, keep peak sets below maximum failure more often so quality stays high.
Junk volume is lots of tired, sloppy reps that add fatigue without clear stimulus. Better fewer crisp sets than endless grindy ones. Use RPE or reps-in-reserve to keep hard sets honest.
Try this: For one lift, fix weekly volume (e.g. 10 working sets). For four weeks, raise load or reps slightly while keeping perceived effort in a narrow band (e.g. RPE 8). Only then add a set or an extra session.