A werewolf, also known as a lycanthrope (from the Greek λυκάνθρωπος: λύκος, lukos, "wolf", and ἄνθρωπος, anthrōpos, "man"), is a mythological or folkloric human with the ability to shapeshift into a wolf or an anthropomorphic wolf-like creature, either purposely or after being placed under a curse and/or lycanthropic affliction via a bite or scratch from a werewolf, or some other means. This transformation is often associated with the appearance of the full moon, as popularly noted by the medieval chronicler Gervase of Tilbury, and perhaps in earlier times among the ancient Greeks through the writings of Petronius.

In addition to the natural characteristics inherent to both wolves and humans, werewolves are often attributed strength and speed far beyond those of wolves or men. The werewolf is generally held as a European character, although its lore spread through the world in later times. Shape-shifters, similar to werewolves, are common in tales from all over the world, most notably amongst the Native Americans, though most of them involve animal forms other than wolves.

Werewolves are a frequent subject of modern fiction, although fictional werewolves have been attributed traits distinct from those of original folklore. For example, the ideas that werewolves are only vulnerable to silver bullets or pierced by silver weapons, or that they can cause others to become werewolves by biting or wounding them derive from works of modern fiction.

-Wikipedia