A piano roll is a music storage medium used primarily in player pianos. It consists of a long strip of paper with holes punched in it, which correspond to the notes of a musical piece. When the roll is fed through the player piano, a mechanism detects the holes and triggers the piano keys to play the recorded music automatically. Piano rolls became popular in the late 19th and early 20th centuries, allowing people to enjoy music without needing to play the instrument themselves. They were often produced by various companies and featured performances by famous musicians, making them a significant part of music history.