A white patch or plaque on a mucous membrane that cannot be characterized clinically or pathologically as any other disease. The diagnosis of leukoplakia is one of exclusion; other conditions such as candidiasis, lichen planus, leukoedema, etc., must be ruled out before a diagnosis of leukoplakia can be made. Leukoplakia may be a premalignant condition. The disease is leukoplakia (Monarch Disease Ontology id MONDO_0043243). Also known as: keratotic plaque.