From the White Wolf Wiki, the most complete White Wolf reference

Ghost Wolves are Forsaken Uratha who do not belong to one of the Tribes of the Moon. They are generally loners who do not feel kinship with the totems or ideals of the Forsaken tribes, and rarely join packs on a more than temporary basis.

This disconnection with werewolf society leads most Ghost Wolves to a transient life, with no territory to call their own and no backup to call upon. They still seek to uphold the oath to Luna, however, and are more likely to hunt down wayward spirits who cross territory boundaries or flee to areas unclaimed by Uratha.

Werewolf: The Forsaken tribes
Tribes of the Moon:	Blood Talons · Bone Shadows · Hunters in Darkness · Iron Masters · Storm Lords
Pure Tribes:	Fire-Touched · Ivory Claws · Predator Kings
Others:	Ghost Wolves · Bale Hounds