Well, there is a saying: "ask 10 werewolves what a werewolf is and you'll get 11 different answers"
My personal opinion as to the definition of a werewolf is something like this: "A werewolf is a human who holds within (in the heart, mind, soul, nature, or whatever) an undeniable (can't be suppressed completely for long) potential for becoming a wolf. This potential may or may not someday manifest in a mental shift and may or may not someday manifest in a physical shift."
In other words, the fact of being a werewolf is not something that is defined by the act of physical transformation. Being a werewolf is one thing, and physical transformation is only a rare side effect of being a werewolf; a side effect that only happens in some, not all, werewolves.
However, the exact definition of "werewolf" is complex enough that most of the rest of this Handbook is absorbed with answering the question "What is a Werewolf", so I suggest you read it.
Please note that the above defenition is old and innacurate, as it only references the (Physical)
Shifting part of werewolves. In reality, there are also
Contherianthropes, you might want to read and understand that before you believe the above definition.
WEREWOLVES (or LYCANTHROPES) The Werewolf, a human in wolf form, sometimes copulates with humans and beasts, but its primary craving is to mutilate, kill and devour. (This is also true when, more rarely, the Werewolf is not a human but an evil spirit animating the body of a real wolf.) Like the conception of the Vampire, that of the Werewolf is bound up with sexual perversions--sadism, necrophagia, necrophilia, etc.--and the Werewolf is also a creature of castration anxieties and incest desires. There are many animals besides the wolf to whom the prefix were- has been applied. These include Werefoxes, Werebadgers, Wereleopards, Weretigers, Werebears, and others. Not all have identical functions or behave similarly. The Chinese Werefoxes, for example, seem to be much closer to the Western incubi and succubi than to the Werewolf. Male and female Werefoxes, in human or animal forms, mate with women and men, respectively. The Werebears of Baluchistan are another variant of the succubus idea. By day they are huge black bears, but by night they become beautiful women who solicit the embraces of men and sometimes hug their human lovers to death during the frenzy of the coition.
Some propose that Werewolves are especially motivated by parthenophagy, or an appetite for the flesh of young girls, which may be sexual as well as cannibalistic. In a rare pamphlet (called "A True Discourse. Declaring the damnable life and death of one Stubbe Peeter, a most wicked Sorcerer") that predilection of Lycanthropes would seem to be exemplified:
"... he would walke vp & down, and if he could spye either Maide, Wife or childe, that his eyes liked, or his hart lusted after, he would waite their issuing out of ye Cittie or town, if he could by any meanes get them alone, he would in the feeldes rauishe them, and after in his Wooluishe likenes cruelly murder them; yea often it came to passe that as he walked abroad in the feeldes, if he chaunste to spye a companye of maydens playing together, or else a milking of their Kine, in his Wooluishe shape he would incontinent runne among them, and while the rest escaped by flight, he would sure to laye holde of one, and after his filthy lust fulfilled, he would murder her presentlye, beside, if he had liked or knowne any of them, look who he had a minde vnto, her he would pursue, whether she were before or behinde, and take her from the rest, for such was his swiftness of foot while he continued a woolf: that he would outrunne the swiftest greyhound in that Countrye: and so much he had pracfised this wickedness, that ye whole Proumee was feared by the cruelty of this bloody and deuouring Woolfe. Thus continuing his diuelish and damnable deedes within the compas of a fewe yeeres, he had murdered thirteene yong Children, and two goodly yong women bigge with Child, tearing the Children out of their wombes, in most bloody and sauedge sorte, and after eate their hartes panting hotte and rawe, which he accounted dainty morsells & best agreeing to his Appetite."
Relevant information
Source:
Slavic Myth and Religion
Werewolf, babies born with a caul, birthmark, or wolfish tufts of hair were believed to be werewolves. The caul was kept as an amulet. Herodotus said of the Slavs (here called Neuri): "There is a custom among the Neuri whereby once a year everyone changes into a wolf for several days, then returns to his original shape."
See also: