Durham rule

[dûrəm]
n.
  1. A 1954 US rule used as a test of criminal responsibility and stating that an individual accused of a crime is not criminally responsible if the unlawful act was the product of mental disease or mental defect.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.