A delusion is a belief that is held with strong conviction despite superior evidence to the contrary. As a pathology, it is distinct from a belief based on false or incomplete information, confabulation, dogma, illusion, or other effects of perception. Wikipedia
Wait, What? What of Faith then? It goes on, Whew!
Many religious beliefs hold exactly the same features, yet are not universally considered delusional. Praise God, Jesus, Allah, Shiva, et al.
How many of us can say that we haven’t been deluded at some time or another?