Playerkilling (or "PKing") is the act of attacking and killing another player in a MUD
, or similar online game.
Playerkilling is a highly divisive issue in these games. Many players consider freedom of interaction to be paramount, and thus support the existence of the playerkiller (or "PK") as part of the milieu of the world. Others prefer not to have players beyond their circle of friends intrude on their gameplay, and thus wish that playerkilling would simply go away. And some people just don't give a shit and like to kill people for the hell of it. As such, many games have attempted to accommodate all sides.
Recently, in the new genre of MMORPGs, Meridian 59 and Ultima Online are known for their laissez-faire stance on PKing (although Meridian 59 created a "safe haven" shard after release, which disallowed player combat, and Ultima Online began a "Renaissance" which split each gameworld into two halves. One half does not allow nonconsensual player combat, and the other is less restrictive.) Other games such as Everquest and Asheron's Call have gone in the other direction, creating "PK Switches" so that those who are interested in player vs. player combat (otherwise known as "PvP") opt in to being able to fight others who have similarly chosen combat. However, both games do offer PvP shards, where all characters are free to attack one another.
This remains possibly the central issue in the world of online gaming, with every new gameworld making its own choices as how to handle the PK.