Vampires (archaic spelling: vampyres) are mythological or folkloric creatures, typically held to be the re-animated corpses of human beings and said to subsist on human and/or animal blood (hematophagy). They are also the frequent subject of cinema and fiction, albeit fictional vampires have acquired a set of traits distinct from those of folkloric vampires (see Traits of vampires in fiction). In folklore, the term usually refers to the blood-sucking living of Eastern European legends, but it is often extended to cover similar legendary creatures in other regions and cultures. Vampire characteristics vary widely between different traditions. Some cultures have stories of non-human vampires, such as animals like bats, dogs, and spiders.

Vampirism is the practice of drinking blood from a person/animal. In folklore and popular culture, the term generally refers to a belief that one can gain supernatural powers by drinking human blood. The historical practice of vampirism can generally be considered a more specific and less commonly occurring form of cannibalism. The consumption of another's blood (and/or flesh) has been used as a tactic of psychological warfare intended to terrorize the enemy, and it can be used to reflect various spiritual beliefs.

In zoology and botany, the term vampirism is used to refer to leeches, mosquitos, mistletoe, vampire bats, and other organisms that prey upon the bodily fluids of other creatures. This term also applies to legendary animals of the same nature, including the chupacabra.

The term vampire can be used to refer to any magical creature of myth that is a predatory parasite, draining power, energy or life from unwilling victims. Mythic creatures who act in this manner are often considered part of the vampire archetype, even if they do not feast on blood.

source: http://en.wikipedia.org