Zombies are animated corpses. A zombie is a type of undead creature, and is similar to (but distinct from) a vampire.
Zombies are generally not sentient, despite usually being created from a sentient being. A zombie usually has no memory of its past existence as a living person.
Zombies usually sustain themselves by feeding on the flesh of living creatures, often of the kind they were created from. Sometimes, these victims themselves turn into zombies.
Depending on the type of zombie, they can either be frail or strong. Regardless, however, as a zombie is not a living creature, it cannot be "killed" in the strictest sense of the word. Some zombies require a headshot to be destroyed, while others require that they be burned to death. Zombies can continue to fight despite the loss of one or more limbs, but usually require the head to function.
Zombies often have regenerative abilities, being able to piece themselves back together.
Similar to vampires, zombies can also have the ability to turn their victims into zombies.
Zombies are usually not intelligent beings. Zombies generally don't have effective fighting skills or the knowledge to operate a weapon, making them easier to fight one-on-one.
Additionally, some zombies move slowly.
As zombies are not living creatures, they generally do not reproduce. Zombies are instead usually created from living creatures. The zombie usually retains no memory of its life as a living being, and is either controlled by a sentient master or exhibits primal behavior.
Raising the dead
Zombies can be created from dead creatures, a process sometimes referred to as "raising the dead." These zombies are characterized by rotting, dirt-caked flesh. This is usually done by a demon or a necromancer.
A zombie can be created from a living creature, a process referred to as "turning" them. This can be done either by another zombie or by some scientific or magical process that wipes the victim's mind.
Types of zombies
Zombies can be categorized by the manner in which they were zombified.
These zombies are created by the use of magic. A wizard who creates zombies by raising corpses is generally known as a necromancer. These zombies appear to be dead biologically, but their body is animated magically, like a puppet.
A lich is a special type of zombie which retains its sentience. Liches are often powerful necromancers who subject themselves to their own magic, with the aim of achieving immortality. Liches sometimes rule over armies of lesser zombies.
A necromancer usually uses an object called a phylactery to store his or her soul, so that it survives the zombification process. In order for the lich to be defeated, its phylactery must be destroyed. Advanced wizards have been known to store pieces of their soul on several different phylacteries, making them harder to destroy.
These zombies were infected by a mind-altering virus or fungus which takes over the central nervous system and eliminates the victim's sentience. The infection can be natural in origin, but is often created as a weapon of biological war. The infection is often highly contagious, but can be prevented with the right medicine. However, there is generally no way to turn these zombies back to their former selves.
Mind controlled beings (either through magical powers, hypnosis, or mind control devices) are similar to zombies in some respects, as their soul is suppressed and their body becomes under the control of a puppet master. Mind controlled beings are not completely zombified, however, as undoing the mind control can restore the victim's personality.
In extreme cases, the same abilities or devices that are used to control a being's mind can be used to destroy it, which could potentially turn the victim into a zombie.