Sanity is a legal term denoting that an individual is of sound mind and therefore can bear legal responsibility for his or her actions and is generally defined in terms of the absence of insanity. It is not a medical term, although the opinions of medical experts are often important in making a legal decision as to whether someone is sane or insane.
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Sanity is sometimes used as an engineering term to mean "internal consistency", as in the phrase "sanity check". This has led to pins on integrated circuits being labeled "LOS": "loss of sanity".
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