Musical notation is any system used to visually represent auditorily perceived music, played with instruments or sung by the human voice through the use of symbols, including notation for durations of absence of sound such as rests. For this reason, the act of deciphering or reading a piece using musical notation, is known as "reading music".
A photograph of the original stone at Delphi containing the second of the two Delphic Hymns to Apollo. The music notation is the line of occasional symbols above the main, uninterrupted line of Greek lettering.