Garou glyph for Gnosis.
Gnosis is similar to the Polynesian concept of mana or the Eastern concept of chi. While all creatures have some spiritual component, Garou can consciously control and use it. Garou are quite literally half-spirit already, and Gnosis reflects how connected they are to that ephemeral other half.
In the Storyteller System, Gnosis is ranked with dots, as well as boxes. The dots are permanent Gnosis while the boxes represent points of temporary Gnosis. A Garou character may not have more temporary points of Gnosis than permanent dots of Gnosis.
Gnosis can be used to bribe spirits, activate fetishes and Gifts, and to enter the Umbra. Creatures without enough Gnosis generally cannot perceive or even enter the Umbra.
Gnosis is a renewable, but dwindling, resource. Garou can regain it at sacred sites, by meditating, or by bargaining with spirits. Sacred sites provide Gnosis, but if they become defiled, the tainted energies can corrupt the Garou, or result in the site no longer producing Gnosis at all.
The water analogy works well here. The Garou need water, but they must also protect their own sources because drinking of tainted waters may make them grow sick, and if they aren't careful, the well may run dry.
Gnosis may be recovered through meditation, or through bargaining with spirits to have them share some of their own Gnosis.
Gnosis may not be spent in the same round as Rage, unless a Gift or other effect specifically requires the spending of both points to activate.
In game, Homid characters start out with the least Gnosis (1), Lupus Characters with the most (5) and Metis characters start out in the middle (3). Kinfolk generally do not have Gnosis, but a special Merit will allow the Kinfolk to do so: 5 points in the Merit is worth 1 Gnosis, 6 points is worth 2, and 7 is worth 3.
A Kinfolk with Gnosis is immune from receiving the Embrace and turning into a vampire. They simply die, which in the eyes of their Kin is far more merciful fate.
Gnosis is the same thing as Chi, Sekhem, and Quintessence. Glamour is a form of Gnosis, just as diamonds are a form of carbon.