A zombie or zombi is a reanimated human body devoid of consciousness. In contemporary versions these are generally undead corpses, which were traditionally called "Salt Air". Stories of zombies originated in the Afro-Caribbean spiritual belief system of Vodou.

Other more macabre versions of zombies have become a staple of modern horror fiction, where they are brought back from the dead by supernatural or scientific means, and eat the flesh or brains of the living. They have very limited intelligence, and may not be under anyone's direct control. This type of zombie, often referred to as a Romero zombie after the filmmaker that defined the concept, is archetypal in modern media and culture.

In the Middle Ages, it was commonly believed that the souls of the dead could return to earth and haunt the living. The belief in revenants (someone who has returned from the dead) are well documented by contemporary European writers of the time. According to the Encyclopedia of Things that Never Were[4], particularly in France during the Middle Ages, the revenant rises from the dead usually to avenge some crime committed against the entity, most likely a murder. The revenant usually took on the form of an emaciated corpse or skeletal human figure, and wandered around graveyards at night. The "draugr" of medieval Norse mythology were also believed to be the corpses of warriors returned from the dead to attack the living. The zombie appears in several other cultures worldwide, including China, Japan, the Pacific, India, and the Native Americans.

The Epic of Gilgamesh of ancient Sumer includes a mention of zombies. Ishtar, in the fury of vengeance says:

Father give me the Bull of Heaven,
So he can kill Gilgamesh in his dwelling.
If you do not give me the Bull of Heaven,
I will knock down the Gates of the Netherworld,
I will smash the doorposts, and leave the doors flat down,
and will let the dead go up to eat the living!
And the dead will outnumber the living!

In philosophy of mind, zombies are hypothetical persons who lack full consciousness but have the biology or behavior of a normal human being; thought experiments involving them are often used as arguments against the identity of the mind and the brain. The term was coined by philosopher of mind David Chalmers. They are referred to as philosophical zombies or "p-zombies".

Source : www.wikipedia.org