ПГМ

Etymology

 * a wordplay between the sound of the РПЦ-abbreviation ("Russian Orthodox Church") and the medical terms like e.g. опухоль головного мозга (a brain tumor).

Proper noun

 * 1)  Absurd, exaggerated Orthodox Christian beliefs and practices, resulting in irrational actions, immorality, violence or unfair politics.
 * 2)  any form of Orthodox Christianity.

Usage notes
Usually used by atheists and by various Russian-speaking Internet users.