Jeju (Cheju) is a Koreanic language spoken in Jeju Province in South Korea. It differs greatly from the Korean dialects of the mainland.
The name is transcribed Jeju in Revised Romanization and Cheju in McCune-Reischauer. In Korean, it is known as 제주 방언 (濟州方言) Jeju bang-eon or 제주 사투리 Jeju saturi "Jeju dialect", as 제주어 (濟州語) Jejueo "Jeju language", or as 제주말 Jejumal "Jeju speech". The last covers both language and dialect.
Although many South Koreans, including those who speak Jeju, consider it a dialect of the Korean language, it can be considered a separate language because it is nearly mutually unintelligible with Korean dialects of the mainland. It has been recognized as a distinct language locally and by UNESCO.
There are 5,000–10,000 fluent speakers, all born before 1950. Jeju was once spoken across Jeju Island, apart from the Chuja islands in the former Bukjeju County (currently Jeju City), where the Chuja dialect, a variety of the Jeolla dialect, is spoken. It also survives in diasporic enclaves in Japan.