1) An officially granted exception to a zoning ordinance. Such exceptions may be granted on a case-by-case basis for some persuasive reason shown.
2) A difference between two statements or other pieces of evidence that usually would be expected to indicate the same thing.
See, e.g. Williamson County Regional Planning Comm'n v. Hamilton Bank of Johnson City, 473 U.S. 172 (1985) (in zoning) and Kotteakos v. United States, 328 U.S. 750 (1946) (between indictment and proof).