Derived from the Anglo Saxan word "Were" meaning Man, combined with Wolf. A Werewolf is a normal human being, but on full moons transforms into a big beastly wolf-like creature, the person tends to lose their mind when they transform, having no control over said beast. In some movies and books such as Underworld the person may be capable of controlling the Werewolf side, it tends to differ from series to series. But generally its very painful to turn into a Werewolf.
Greg stared up at the glistening radiant full moon, not caring to notice his best friend Steve had begun screaming in pain and agony, his clothes were ripping, his fingernails were growing long and pointy, his face began to lengthen and form something simillar to a snout. Greg knew he'd better get out of there, and fast, before his Werewolf friend turned on him.