Nashville number system
n.— «On a legal pad he had “charted” the five songs, using what’s called the Nashville number system, a time-saving trick that assigns a number to each chord in the do-re-mi musical scale, making it easier for musicians to change keys without rewriting the chart. We listened to my originals one by one.» —“When Walter Mitty Met Conway Twitty” by Bob Baker New York Times Mar. 25, 2007. (source: Double-Tongued Dictionary)
Further reading
Mary Beth in Greenville, South Carolina, wonders: Why do we say four-oh-nine for the number 409 instead of four-zero-nine or four-aught-nine? What are the rules for saying either zero or oh or aught or ought to indicate that arithmetical symbol...
David says that when he was growing up in Akron, Ohio, his family referred to the grassy area between the sidewalk and street as the devil strip. He’s since moved to Nashville, Tennessee, where he doesn’t hear that term. There are lots...