jargon: Zone of Control: The area directly influenced or controlled by a person or thing. In computer games like Civilization, this may mean "adjacent hexes", giving rise to the rule:

Units may not move between squares which are both within ZOC of enemy units.

In LARPs, this is the area directly affected by a person or object. The MIT Assassins' Guild normally defines ZOC as the distance between two people such that they can touch each other's hands when outstretched; approximately one fathom. Extensions to ZOC include item ZOC - the distance between a person and an item such that the person can touch the item; and Double ZOC - the distance between two people such that there exists a point between them that a normal sized person could stand in and be simultaneously within ZOC of both people.

Usage:

Abilities
"To heal someone one HP, you must stand within ZOC and cast the Heal spell"
Effects
"Rockets cause ten HP of damage to everyone within ZOC of the impact point"
Rules
For safety, do not enter into ZOC of an enemy player.