High volume puncher can equate to a boxer throwing a high volume of punchers throughout each round in a 12-15 round bout. High workrate can mean the same as the above, but you can also include other factors, high workrate in footwork, head movement, etc, etc over 12-15 round bouts.
Volume puncher is a guy that tries to stop his opponent by wearing him down with a lot of punches, like Joe Calzaghe or Vitali Klitschko (especially the comeback version). High workrate is pretty self explanatory.. A guy that does a lot in the ring.
Lots of punches, typically not with power. The advantage they gain tends to be with judges who score activity rather than productivity far too often. A high workrate would be anybody who throws much more often than normal guys in their weight class. Joe Cal is an excellent example. His "punches" were typically thrown with horrible technique but almost twice as often as his division's normal rate.
Timothy Bradley Amir Khan Younger Pacquiao (but with power) Lower the weight class the higher the workrate and volume. High workrate + power + banger/brawler boxers = war
