4B or "Four Nos" is a feminist movement that originated in South Korea. The name refers to its defining four tenets which all start with the Korean-language term bi. The prefix bi- is Sino-Korean in origin, functioning similarly to the English prefix “un-“ or “non-“. Because it sounds like the letter “B”, the movement’s name works simultaneously as a number and an acronym. Its proponents do not date men, marry men, have sex with men, or have children with men. The movement emerged between 2017 and 2019 on Twitter and on the website WOMAD. It has since spread internationally, namely to the United States after its 2024 presidential election.