A compact disc (usually called a CD) is a flat, circular piece of plastic about five inches across that stores digital information. The disc has a shiny, reflective surface that looks almost like a mirror, and tiny patterns etched into it hold music, computer programs, photos, or other data.

CDs work by spinning inside a special player while a laser beam reads the microscopic bumps and flat areas on the disc's surface. These patterns translate into the ones and zeros that computers and music players understand. A single CD can hold about 80 minutes of music or 700 megabytes of computer data.

Invented in the early 1980s, CDs revolutionized how people listened to music. Before CDs, most people used vinyl records or cassette tapes, which wore out over time and could get scratched or tangled. CDs offered crystal-clear sound quality that didn't degrade, and you could skip instantly to any song instead of fast-forwarding through tape.

Your parents or grandparents probably owned hundreds of CDs, carefully stored in plastic cases with album artwork. Today, most people stream music from the internet instead, but CDs are still used for important purposes like archiving data, distributing software, and releasing music for collectors who want a physical copy.