Out of key | definition of out of key by Medical dictionary
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key a character of special significance in an organism. Such characters are used in a system for determining the identity of an organism on the basis of the presence or absence of a succession of characters. Usually such keys are DICHOTOMOUS (2); that is to say, at each step there is a choice between two possibilities. Keys, however, may have more than two characters at each step and there is a gradual elimination of absent characters until identification is made.