The term MUSICAL LINES can be solved by the crossword solution STAFFS, which is a six-letter word. A staff is a set of five horizontal lines and four spaces that is used in music notation to organize written music. It is also known as a stave. The staff is used to represent the pitch and rhythm of a piece of music. Each line and space on the staff corresponds to a different note. Notes are written on the staff using clefs, which indicate the pitch of the notes.