Multihit allows the player to hit zombies in groups with a melee weapon instead of only being able to hit one at a time. This makes protecting yourself against a horde of zombies much easier and also much more fair. Here's what exactly it does and how to enable it on your server.
1. Open the Advanced Server Settings tab
2. Under pzserver_SandboxVars.lua, find the line that says MultihitZombies
3. Set this to true