The P'o (pronounced roughly p-ho) is the lower soul of a creature. The exact nature of a P'o varies based on the particular creatures' view points, within the World of Darkness.
Wraith: The Oblivion Edit
The P'o is a specific attribute of ghosts of the Yellow Springs in Wraith: The Oblivion. It is effectively an Asian wraith's Shadow, but is generally more tradition-bound and more concerned with protection of the body rather than the active nihilism of its western counterpart. Some wraiths can actually exist with a p'o alone but not be a Spectre; these are called hungry ghosts, or kuei.
Kindred of the East Edit
In Kindred of the East, a Kuei-Jin's P'o is an archetypal personality, serving the same function as a wraith's Shadow, or a Cainite's Beast. In addition, all Kuei-jin characters (and dhampyrs) have a P'o attribute, which governs the strength of the lower soul relative to the higher soul. Spirits in Kindred of the East books are given a P'o rating that corresponds to the Rage rating of spirits in Mage and Werewolf books.