A Bone Shadow werewolf is a shaman of the Uratha. They have sworn to Death Wolf to pursue the secret lore of the spirit realm. Their oath is to “Pay each spirit in kind.” A Bone Shadow’s curiousity leads them to make pacts with the spirit realm.

from p27 of Werewolf: the Forsaken by White Wolf

The Bone Shadows—Searchers in the dark places who seek to understand the spirit world that is denied them. Theirs is a winding path of wisdom, teaching the necessity of understanding the many threats that emanate from the Hisil.

Note:This is only a scrap of information. For more detail, buy the book and RTFM.