Zone of control

[jezuskryst]

In the Civ3 Editor, on the Units page, there is a box titled 'Zone of Control'. I don't know what this means. When I look it up in the Help, I get the remarkably helpful answer of:
Zone of Control (Unit Statistics)
Determines whether or not the selected unit exerts a zone of control.
Could somebody tell me what exactly this means?

[zulu9812]

The unit gets a free 'attack', of sorts, at units that move within one square of it, taking the enemy unit's HPs down by one. However, it won't attack every unit that moves within one square, but most of them I'm not sure what the ratio is.