A ZEP (or Z.E.P.) is an abbreviation for a Zombie Escape Plan. A ZEP is made in the event of a zombie apocalypse, in order to prolong chances of survival, and are definitely crucial. If you haven't made a good ZEP yet, hurry up.
Survivor: "I'm so glad I thought to make a ZEP, if I hadn't I might've end up like Brad..."
Brad/Zombie: "ARRRGHRRRRRRROW! BRAAAAAAAINSSSSS!"