staff
theorystaf
A set of five horizontal lines on which musical notation is written.
The staff (plural: staves or staffs) is the foundation of Western music notation — five horizontal lines and four spaces on which notes are placed. Higher positions represent higher pitches. A clef at the beginning fixes the exact pitch mapping.
Notes above or below the staff use ledger lines. The grand staff for piano combines treble and bass clefs. The five-line staff was standardised by the 11th century.
Before the five-line staff, systems used one to eleven lines. Guido d'Arezzo's four-line staff for plainchant is still used for Gregorian chant today.