Roll-
playing, which takes its
name from the occasional
player who is so confused that he actually spells "
role-playing" this way due to his
obsession with the
parts of the
game that center around
dice, is the
act of playing an
RPG as if it were simply some sort of
hack-and-slash game in which the only
object is to kill things and gain
experience points,
levels, better
stats or
equipment, or other such things. In short,
roll-players strive to "win"
RPGs.
While there is something to be said for this kind of play, if one wants to do this exclusively, there are plenty of single-player video games that allow this -- and plenty of MUDs that are PK havens for those who want to compete against fellow humans RPG-style. What makes a role-playing game with humans unique is the opportunity to pretend together.
Roll-players are also called munchkins or powergamers -- though keep in mind that some people who enjoy high-powered player characters actually role-play.