Pitching gem, in baseball slang, is a term used to describe an exceptionally talented pitcher. The crossword solution for this term is NONO, which is an acronym for 'No-Hit No-Run'. This phrase is used to describe a pitcher who has thrown a complete game without allowing any hits or runs. This is considered a rare and impressive feat in baseball, and thus the term 'pitching gem' is used to refer to a pitcher who has achieved this feat.