Pareidolia is a type of illusion or misperception involving a vague or obscure stimulus being perceived as something clear and distinct. For example, in the discolorations of a burnt tortilla one sees the face of Jesus Christ. Or one sees the image of Mother Theresa or Ronald Reagan in a cinnamon bun or the face of a man in the moon.
Those are, I believe, the most common contexts in which the phenomenon crops up: religion and astronomy. I learned the word from astronomer Philip Plait, who’s sick of this sort of thing, especially as put forward by Richard Hoagland:
He’s had enough of Hoagland’s assertions that NASA is covering up evidence of extraterrestrial life, that the infamous Face on Mars was built by sentient aliens and, of late, that otherworldly machine parts are embedded in the red planet’s dirt.