"오선지" refers to a five-line staff used in music notation. It serves as the foundation for writing musical notes, allowing musicians to read and interpret music accurately. Each line and space on the staff represents different pitches, making it essential for composers and performers. In Western music, the staff is often accompanied by clefs, such as the G clef or F clef, which indicate the pitch range of the notes. The use of the five-line staff has been a standard practice since the Middle Ages, facilitating the development of complex musical compositions across various genres.