Player versus player (PvP) is a type of multiplayer interactive conflict within a game between human players. This is often compared to player versus environment (PvE), in which the game itself controls its players' opponents. The terms are most often used in games where both activities exist, particularly MMORPGs, MUDs, and other role-playing video games, to distinguish between gamemodes. PvP can be broadly used to describe any game, or aspect of a game, where players compete against each other. PvP is often controversial when used in role-playing games. In most cases, there are vast differences in abilities between players. PvP can even encourage experienced players to immediately attack and kill inexperienced players. PvP is often referred to as player killing in the cases of games which contain, but do not focus on, such interaction.