I suppose your definition of a perfect burst is a 100% lethal one. Thats fine. By using the term, i'm merely giving reference to one that mortally wounds someone with a 1-2 second window where 1 followup hit will finish them off (where a crit during said burst didn't occur for example.) Doesn't even have to be a burst at all. You coulda been the tank slugging it out with a dps and all cd were exhausted. You're about to land the killing hit and some random dps just pops out and finishes it.