What is Black Letter Law?

Legal Definition
In common law legal systems, black letter laws are the well-established technical legal rules that are no longer subject to reasonable dispute. Some examples are the "black-letter law" of contracts or the "black-letter law" of trademarks. Black-letter law can be contrasted with legal theory or unsettled legal issues.
-- Wikipedia
Legal Definition
Basic standard rules that are generally known and free from doubt. The black letter law on any subject consists of rules that can be applied in a very mechanical way without moral qualms or other considerations.