Hey.
The variables refer to the PZServerSettings' dropdown menu, from top to bottom.
For instance "Zombies = 3" is normal zombies. While "Zombies = 1" is insane zombies, and "Zombies = 5" is none.
In the steam version PZServerSettings can be found at steamapps\common\ProjectZomboid\PZServerSettings\.
I hope I made sense.