[ericthered]

In the realm of fiction, monsters generally have archetypes, not taxonomies. You compare the distinguishing features of the archetype to the monster you have to determine if it should be called by the archetype name. This means that drawing lines between archetypes is usually pointless, though contrast isn't useless.

A mummy is a kind of corpse. Mummies exist, and Undead using such a corpse are usually referred to as mummies, regardless of any other factors. Of note is some of them have features not shared by other undead.

Zombies are tricky because they have at least two archetypes in modern lore. One is the drone following the will of a sorcerer (or occasionally a curse). The other is a corpse animated by psudeo science and craving brains. Making things more complicated is that While zombies typically lack both a healthy body and a functioning mind, missing either one will suffice to acquire the title. They also tend to be the fallback name for corporeal undead.