Passive zombie

From The Urban Dead Wiki

A Passive zombie is a zombie which does not actively attack survivors and doesn't seek to progress as a zombie.

This is an in-game observation that stems from the behavior induced by players who rather play as a survivor. Passive zombies seek revival, often congregating at revivification points or wait at a set location for a reviver to come to them using metagaming.

Another slang term that has arisen from this observation of behavior is "Mrh? Cow".