, mirror ball, glitter ball, ball mirror, crystal ball, or specular sphere is a roughly spherical object that reflects light directed at it in many directions, producing a complex display. Its surface consists of hundreds or thousands of facets, nearly all of approximately the same shape and size, and each having a mirrored surface. Usually it is mounted well above the heads of the people present, suspended from a device that causes it to rotate steadily on a vertical axis, and illuminated by spotlights, so that stationary viewers experience beams of light flashing over them, and see myriad spots of light spinning around the walls of the room.
What are now sometimes called "disco balls" were first widely used in nightclubs in the 1920s. They were already in existence and use before then, appearing in a description of a ballroom dance in 1897 in Boston. An early example can be seen in the nightclub sequence of Berlin: Die Sinfonie der Gro▀stadt, a German silent film from 1927. In the 1960s, 1970s and 1980s, these devices were a standard piece of equipment in discotheques, and by the end of the 20th century, the name "disco ball" had grown quite popular.