Player versus environment

Player versus environment, (or PvE, sometimes player versus monster, or PvM), is a gameplay distinction, in contrast with player versus player (short: PvP) gameplay.

Player versus Environment is a type of gameplay common to RPGs in general. This is where the character engages in combat with AI-controlled computerized opponents, as opposed to PvP, where she/he/it engages with human players as opponents.

In Guild Wars, PvE content is available to roleplaying characters. However, a PvP character can engage a set of computer controlled opponents as well as other players. In PvE gameplay, your primary purpose (aside from fun, obviously) is to "grow" your character, gain experience, learn skills, acquire better weapons and armor, etc. This is done mainly by completing quests and missions, and by venturing into explorable areas to fight monsters.

Controversy
There are some who worry that the slaying of endless AI mobs could be considered a form of animal abuse, if in fact the mobs are living beings. As the definition of what defines a living being evolves, there is certain to be more debate on this pressing issue.