From Path of the Vampire Wiki
Zombies are husks brought to life by the return (either accidental or forced) of a spirit to a dead body. The being is only classed as a zombie when it is incapable of cognitive reason beyond instinct, and thus becomes a mindless monster even though the spirit has returned.
A zombie can, technically, range from being a near-skeleton, completely devoid of flesh, to a recently-dead corpse which has suffered brain death. Any body which has not yet suffered brain death cannot be classed as a zombie, as it would almost certainly retain desires beyond the need to feed.
Any true zombie is driven by the most primal of urges; the instinctive need to feed. As their body is in the active process of decay (which is not prevented by the return of their spirit), hunger is practically all they feel. They are unable to reason, communicate, or think at any real level. They are below even the intelligence level of animals.
Thus, though their spirit may inhabit their body and force it to move around (as a puppeteer moves around a puppet), the zombie has no part of its former human self remaining within it. No memories, no emotions, there is nothing but the overwhelming desire to fill their decaying stomachs with anything they can find (which most commonly includes the flesh of others).
A zombie cannot feel pain, and can survive anything but the most crippling of injuries. They are also stronger than the average human, but are much slower due to the onset of rigor mortis.
It is unknown whether a zombie's "death" causes their mortal spirit to return to the Shadow Realm, some other plane of existence, or if it stays in the broken shell of the zombie for all eternity.