Definition & Meaning of "flat-earther"in English

What is the origin of the term "flat-earther" and how is it used?

"Flat-earther" is a term that dates back to at least the 19th century, originally describing people who literally believed the Earth was flat. Over time, especially in the late 20th and early 21st centuries, it broadened into a metaphor for anyone who denies established science or embraces conspiracy theories, emphasizing stubbornness and rejection of evidence. It is most often used in informal, critical, or humorous contexts, appearing in media, social media, and debates about science denial. The term is derogatory in intent but can be context-dependent, sometimes applied jokingly rather than as a serious insult.