A person that believes the earth is flat. A flatearther believes NASA is a government agency that hides the truth of the flat earth with lies, fake photos, and videos of space. One believes the sun and moon are directly overhead with a diameter of roughly 30-70 miles across. Flathearther's typically suffer from the Dunning-Kruger effect.
Sarah: "I wonder how the orbit of the ISS is around the world! You know the world is flat so the orbit should be strange."
Mike: "HOW MANY TIMES DO I NEED TO TELL YOU, THE EARTH IS NOT FLAT, YOU FLEARTHER"
Overencompassing name for the company of FlaatterCo, a tasty bit of booze for all the liver-killers out there. Also is the parent of the offshoot cult, the TenancyAgreement. Google it