A dance organ is a big machine that makes music using pipes and buttons. It's kind of like a giant keyboard that you can dance to! When someone presses a button on the organ, it makes air go through a pipe, which creates a sound.
It's called a dance organ because people used to dance to the music that it made. It was a fun way to have music at parties and events before there were things like speakers and radios.
Nowadays, dance organs are often used for entertainment or as a special feature in museums or historical sites. They are still really cool to see and hear!