An unproven theory, thought or idea that often has a large amount of evidence pointing contrary, usually used in a form of humor, satire or sarcasm. It is often used to convey in text messages the content is not to be taken seriously.
"I just bought a Birds Aren't Real Hoodie"
"That is some nice tinfoil."
"Christopher Columbus fell off the flat earth in 1492, and was reinstated in our history by aliens to keep us complacent in thinking the world was round *tinfoil intensifies*"