@zebratron2084 in WoW it's referred to as "overheal," and Serious Raiders (lolololooooollll) track it Very Seriously because overheal is Wasting Mana and therefore BADSAUCE.
in D&D they can sometimes "roll over" and become "temporary hit points"--raising your HP total from 45 to 50, until you get hit for 7 points of damage, then your HP total is back to 45 but you're only down 2 points instead of 7. temporary HP usually wear off if you sleep or rest, or at the end of the spell duration.