Definition of tenderloin
1the tenderest part of a loin of beef, pork, etc., taken from under the short ribs in the hindquarters. the undercut of a sirloin. 2 informal a district of a city where vice and corruption are prominent.
[ late 19th century: originally a term applied to a district of New York, seen as a 'choice' assignment by police because of the bribes offered to them to turn a blind eye]