(Cheryl of the Clue Crew chimes in about musical notation.)   It's the bookkeeping term for the lines above and below the musical staff
[DOC] [TLE] Coudal Archives Film and Television [PAR] "But high on anyone's list of associations with this film is the music of Leonard ..... 
NFL Films' highlight reel from a crew shooting the Super Bowl on vintage Kowa 
...... "The term 'red line' implies the color of the line to be red.