The Invisible Pink Unicorn (IPU) is the goddess of a parody religion used to satirize theistic beliefs. She takes the form of a unicorn that is paradoxically both invisible and pink. Because of that IPU is used to argue that supernatural beliefs are arbitrary. The Invisible Pink Unicorn being is used to point out that because she is invisible, no one can prove that she does not exist or even that she is not pink. The IPU is an illustration which attempts to demonstrate the absurdity of citing attributes and a lack of evidence as proof of a deity's existence.
She is often used as a rhetorical illustration by atheists and other religious skeptics as a contemporary version of Russell's teapot. Invisible Pink Unicorn is also often mentioned in conjunction with the Flying Spaghetti Monster.