not guilty by reason of insanity

: a plea by a criminal defendant who intends to raise an insanity defense —used in jurisdictions that require such a plea in order for an insanity defense to be presented

: a verdict rendered by a jury in a criminal case that finds that the defendant was insane at the time of committing the crime as determined by application of the test for insanity used in the jurisdiction — compare guilty but mentally ill

Note: A verdict of not guilty by reason of insanity usually results in the commitment of the defendant to a mental institution. Such a verdict, however, may allow the defendant to be released, sometimes into the custody or care of another (as a family member).