A thought that you believe to be true. The "facts" are completely fabricated and are supported by zero empirical evidence whatsoever. The only qualifier is that you believe the fact to be true.
Jordon: "Fact: fat people have less body hair than skinny people."
Kara: "that's not a fact."
Jordon: "yes it is."
Kara: "supported by what evidence?"
Jordon: "My observations. Brain fact!"