Kill On Sight was originally a term used in the Rogues Gallery (Brainstock) for a Pker with more than 15 Bounty points placed on them. To have the "bounty points" removed, the offender must have their bounty claimed by a Bounty Hunter. Once a user on the Rogues Gallery had under 15 bounty points again, the KOS status was lifted. Despite this, modern-day Bounty Hunters kill offenders on sight regardless for the Bounty anyway.
Since this, several groups from 2008 onwards have used the term KOS under their own terms and requirements. It is most usually used as a status for users who have PKed one or several members of the group.
Because of UDWiki's policies, groups are free to place whoever they want on their personal KOS list. Because of this, many conflicts arise between groups or players who believe they've unfairly been placed as an enemy and want to be removed. Unfortunately, because of the previously mentioned freedom, it is mostly within any groups right to maintain their own "enemies" and "KOS" lists, even if the authority may be abused from time to time. It is in every reader's interest that UDWiki groups should always be read with the author's point of view taken into account.