Excellent question, d, and it's a difference all Doms should know!

One good definition of punishment I read on here is that it should be something given reluctantly that neither partner relishes, so it's genuinely given to change unacceptable behaviour. If the sub enjoys it and behaves so she gets it, if the Dom relishes giving it - it's lots of things but that's not actually punishment.

I am currently renegotiating this very concept with my Master as I've realised it's not helpful to me to think of what he does to me as 'punishment' when it's actually a means for me to submit profoundly to him - a behaviour he definitely does not want to punish out of me!