Zombie are one of the five known types of monsters. They are presumably the most numerous of the monsters, and appear to inhabit much of the land.
In The Pocalypse the zombie epidemic began several years prior to the beginning of the comic's storyline. It is unknown what triggered it.
Generally a zombie is a human who has been infected with the zombie virus, which is spread via a bite from a zombie. Once bitten a human will succumb to the virus and become a zombie. Vampires are also susceptible to the virus, infected vampires becoming zompires. Mutants however are poisoned by the bite.
Zombies are characterized by their green decaying skin, yellowed teeth, extended arms and primitive communication skills. Zombies show no noticeable strengths, essentially being mindless. They can prove a threat when encounter in larger groups (as is often the case).