白痴（英语：Idiot），是源自希腊字的Idiotos，意指无法在公共生活上承担责任的人。

学者症候群（Idiot Savant）一词是一百多年前由英国医师兰登·道恩（Langdon Down）所创用，当时「白痴」（Idiot）一词只用以描述智力功能极低的儿童，并没有很强烈的负面意义，是可以接受的医学与心理学名词。尽管近三四年来，智能障碍之定义迭有新解，但「白痴」一词是指现今教育界、心理学界、医学界与社会学界所谓重度与极重度者，殆无疑义。

19世纪开始的医学与心理学将白痴这个词定义为「严重的智能不足」，智商低于80（IQ的标准差为18）。因为一般将「白痴」一词作为羞辱用语，用作骂人愚蠢、能力差，此一词不再作为正式用语。

An idiot, dolt, dullard or (archaically) mome is a person perceived to be lacking intelligence, or someone who acts in a self-defeating or significantly counterproductive way. Along with the similar terms moron, imbecile, and cretin, the word archaically referred to the intellectually disabled, but have all since gained specialized meanings in modern times. An idiot is said to be idiotic, and to suffer from idiocy. A dunce is an idiot who is specifically incapable of learning. An idiot differs from a fool (who is unwise) and an ignoramus (who is uneducated/an ignorant), neither of which refers to someone with low intelligence. In modern English usage, the terms "idiot" and "idiocy" describe an extreme folly or stupidity, and its symptoms (foolish or stupid utterance or deed). In psychology, it is a historical term for the state or condition now called profound intellectual disability.