The Nashville Numbering System (NNS) is a musical notation system used primarily in the context of popular and country music to describe the chord progressions and relationships within a song. It's a versatile method that allows musicians to communicate and transpose musical ideas quickly and easily, making it particularly useful in studio sessions, live performances, and collaborative songwriting.

 

Rather than using traditional chord names (like C major, G minor, etc.), the Nashville Numbering System assigns a numeric value to each chord based on its position within a given key. This numeric value corresponds to the scale degree of the chord within that key.