From publisher blurb:
Idols exist in many cultures, even if you don’t recognize them. A bronze bull, a triangle with inset eye, a malformed human body; all of these are representations of ideas worshiped in some way or another. But even among these symbols there exist ones with ties to dark forces and old ways. These vile idols draw power from primal influences, like darkness, the cold, and even blood.
Vile idols are essentially intelligent artifacts, and these three examples expand on the concept of idols in the Pathfinder Roleplaying Game that hold power and influence, either from absorbing dark energy, or channeling it.