A zombie is a dead person that is brought back to life through a curse (voodoo, necromancy) or a mutation and has recovered some vital functions like movement.

They are near-mindless, possessing little reasoning power, though many can perform "remembered behaviors" from their mortal existence.

Zombies are omnipresent in the folklore of Haïti, where they are created by voodoo, an african type of black witchcraft. More recently, zombies films have exposed new theories according to which man-made virus or genetical experiments are held responsible for the creation of zombies. Such films put a strong emphasis  on flesh and blood : rotting bodies and their attendant maggots, as well as the still-warm gore resulting from savage, often cannibalistic attacks upon the living.

Zombies have been confused with many other monstrous creatures. Monstrous will try to make a clear distinction between the different entities that proceed from death.

Some zombies have the appearance of the living but their lack of free will and souls give them the appearance of mechanical robots.

Other display visible signs of desiccation, decay and emaciation on their face and body. They have blank, expressionless faces that become more animated when they get hungry  and engage in a feeding frenzy.

They are incapable of speech, but often tend to make moaning and guttural sounds. They are normally encountered wearing whatever clothing they wore in their human life, prior to reanimation.

Zombies never sleep, and they are incapable of fatigue.
Zombies are impervious to pain and require no air to breathe.
They are thus immune to drugs, poisons, gases, extremes of temperature and pressure, high voltage electricity, suffocation, and drowning.  
While not invulnerable to physical injury, zombies can suffer great damage to their bodies (including dismemberment) without being adversely affected. Dismembering the legs will render the zombie immobile, but the creature will still continue to subsist. Likewise, decapitation will incapacitate the body, but the head will still "live".
Zombies don’t possess any superhuman strength, nor do they have a night vision, a characteristic usually common to undead monsters.

“walk or die” has been replaced by “die and walk”. The most terrific aspect of the zombie is that it first appears as the casual shape of a typical civilian which mind has been sucked out and left empty. Zombies are terrific because instead of delicately sucking your blood  as the vampire, they come in disguise and brutally tear you into pieces. The deactivation of a zombie's nervous system, caused by the curse or chemical and genetic alterations, has often been used to explain their very low mobility and rate of metabolism. The chemicals in the human hypothalamus acts as a stimulant for their metabolism, prolonging their not-quite-dead condition.

Zombies created by voodoo tend to be harmless, and are often used as slaves by the witch doctors that have created them. In spite of its rather feeble intelligence, the hollywood zombie is a both intellectually and physically driven only by his all-consuming hunger for fresh human flesh. Why the dead are so hungry for living flesh is still unclear?. As a slightly potty researcher illustrates in Day of the Dead, the dead do not need to eat, they reach for live flesh even when they have no mouth or gullet, even when their stomachs have been removed. The impulse is part of their very fibre, a spiritual craving. They are dead, and death wants to consume life. It is an image of insatiable nihilism that is hard to resist. In Romero’s trilogy and sequels, the world has discovered that these zombies are particulary fond of human brains, requiring the chemicals in the hypothalamus for maintaining their existence.

Some cases of vampiric zombies have also been recorded.

Zombies are also known to locate easily their preys across walls and distance. Do they smell living flesh like our Ogre of the fairy folklore ?