The term 'OLD PIANO TUNE' can be summarized by the crossword solution 'RAG', which is a three-letter word. Ragtime is a musical genre that originated in the United States in the late 19th century. It was popular until the mid-1920s and has since become a historical musical style. Ragtime is characterized by syncopated rhythms and a syncopated melody, often played on the piano. It is considered to be the precursor to jazz music.