A zombie is a mythological undead corporeal revenant created through the reanimation of a corpse. Zombies are most commonly found in horror and fantasy genre works. The term comes from Haitian folklore, in which a zombie is a dead body reanimated through various methods, most commonly magic like voodoo. Modern media depictions of the reanimation of the dead often do not involve magic but rather science fictional methods such as carriers, radiation, mental diseases, vectors, pathogens, parasites, scientific accidents, etc.
Faces of apocalypse, as I'd summarize from the rawly acquired Wikipedia article.
Continuing from the note, I apparently have a quirk on asking why Mikoto Arakawa was a zombie.
What kind of zombie was Mikoto Arakawa when abiding to her reanimation, it's obviously fantastical: either voodoo or necromancy, and weirdly pitched as a third runner, Chaos Magic. I'd rather be more fond of her being a jiangshi, but it was clearly not the case at all.