An undead that rises from the grave during the night to drink the blood of the living in order to stay "alive". Generally the word "undead" refers to a creature that should be dead but is still active within the realm of the living.

The word "vampire" comes from the Slavic word obyri or obiri, which evolved into the Bulgarian word "vampir". Although sources differ greatly, some say that the Greek word nosophoros (which means "plague-carrier") that evolved into the Old Slavonic word "nosufur-atu" is a synonym for the word "vampire". In our culture, the words "vampire" and "nosferatu" are interchanged often.
 

Birth of a Legend
The vampire is truly a global creature, with myths related to the dead which rise to drink the blood of the living coming out of cultures all around the world. From Africa to Japan to Spain and the UK, the vampire has held humans enthralled for centuries. Nowhere, however, do we see more vampire folklore than in the stories of the Slavic people. Perhaps the reason for this is the historically high population of gypsies in that area. The migration of the gypsies has been traced back across the continent to northern India, where the religion had a cast of certain bloodthirsty deities (such as Kali) and creatures (such as a bhutu). It has been theorized that with this as a base of folklore, the gypsies picked up bits and pieces of other legends as they migrated toward the north-west and as a result, altered the folklore of the Slavic nations.

According to legend, the victims of a vampire either dies or becomes a vampire. Vampires could also be made in a variety of ways: a child born under certain omens, a cat or other animal jumping over a dead body, someone who committed suicide, and practising witchcraft are some activities thought to be the cause of vampirism. Even inanimate objects and animals were thought to be able to become vampires: pumpkins, watermelons and other fruit that was left out past a certain amount of time, latches that were left unlatched too long, dogs, horses, sheep and snakes are among the objects with vampiric potential in older superstitions of the Slavic gypsy community.

Vampires were thought to be able to take the form of a bat, or many other animals, as well as a mist. They were able to control creatures like rats and wolves, and the elements were at their command. Some kinds of vampires were thought to be endowed with the ability to fly. Most all vampires of legend slept either in coffins, or returned to the earth to sleep in their grave. Among other superstitions, vampires were supposed to need to return to the earth from their homeland each night, could not cross running water, could not see their reflection in a mirror, could not enter a place uninvited, and could not tolerate the symbol of the Christian crucifix.

In order to protect yourself from a vampire, the cross or crucifix was thought to be very powerful in the Christian countries. Little is known of how holy symbols were used as vampire protection before the Christian era, however, folk-cures were often employed. Garlic was the most popular vampire repellent, as well as hawthorn and the mountain ash (rowan). Another defense was scattering seeds - vampires were supposed to become so involved in counting every single seed that they would either lose interest, or be caught counting even as the sun came up. Surprisingly, silver was not as traditional a protective metal as supposed in popular fiction - iron was the material of choice. Iron shavings were placed beneath a child's cradle, a necklace with an iron nail was worn, and other iron objects were placed strategically around the place needing protection.

Once a vampire was discovered, it could be destroyed by cremation, cutting off its head, exposing it to sunlight or by driving a stake through its heart. Other superstitions told that a vampire could be destroyed by touching it with a crucifix, drenching it in holy water and garlic, stealing his left sock, filling it with stones and throwing it in a river, or using a "dhampir", or a vampire's child. Dhampirs were allegedly the only people who were able to see invisible vampires, and they often took advantage of this by hiring out their services as vampire hunters.
 

In Literature
Vampires were popularized by the Irish author Bram Stoker with his story of Count Dracula, a Transylvanian vampire, in 1897. The story was probably based on Vlad Tepes, a medieval character of exceptional bloodthirst. He supposedly impaled his enemies (hence his nickname Vlad The Impaler) and cut off their heads. He ruled Walachia as Vlad III in the 15th century, which is now part of Romania. He signed his letters with Vlad Dracula, which can be translated as Vlad, son of the dragon or son of the devil. His father was called "Dracul" because he had a dragon depicted on his coat of arms.

Before Stoker, vampire literature was rare, but existent. Perhaps the most popular pre-"Dracula" stories were "Carmilla", by J. Sheridan Le Fanu; "Varney The Vampire", by James Malcolm Rymer; and "The Vampyre; A Tale", by John Polidori.
 

Modern Vampires
Vampires today, as they are often portrayed in modern day literature, are much different than the vampires of old. They do not necessarily have the same limitations the vampires from legends had. Garlic and crosses offer no protection against them, they are supposed to be able to walk during the day, and sometimes are not considered to be undead, but another species of humans. They usually still have extraordinary powers: their strength and speed surpasses that of humans, and their senses are heightened to a preternatural level. The need for blood, however, has not diminished, in spite of how we have seen in the last twenty years a trend toward a conscientious vampire who is tormented by his/her own humanity.

Credit for many of the modern innovations with the vampire myth must go to Anne Rice, who is the author of the immensely popular "Vampire Chronicles", a five book series concerning a vampire named Lestat. The first book from the series, "Interview with the Vampire" was made into a movie in 1994, and joined the ranks of many other vampire movies made over the decades. Bela Lugosi will always be remembered as the first Count Dracula on the big screen, and he is primarily responsible for the popular wealthy aristocrat appearance, black cape, fangs, widows peak, and Transylvanian accent that is so characteristic of the vampire stereotype.

Breathing un-life into the vampire culture recently has been "Vampire: The Masquerade", a role-playing game published by the company White Wolf. Done in a Dungeons & Dragons fashion, people gather to develop vampire characters within the guidelines, and then successfully carry their character throughout a "story" according to the rules. "Masquerade" enthusiasts often gather in small groups or in large organized story-telling sessions to actually become a living part of the vampire legend.
 

Source - Encyclopedia Mythica