A zone is defined as an area where you can attack each other in close combat. Stepping back and forth, dodging each other, etc. is included, you are not confined to an arms length of each other. So for example a normal sized bedroom could be a zone, you can stand at opposite walls from each other out of reach, but you would still be close enough to attack directly. If you were entering from the next zone, for example the hallway, you would be at a disadvantage, because you would have to get inside first.
