An optical disc is a flat, circular medium used to store digital data. Common types include CDs (Compact Discs), DVDs (Digital Versatile Discs), and Blu-ray discs. These discs are read by lasers in devices like CD players, DVD players, and Blu-ray players, which interpret the data encoded in tiny pits on the disc's surface. Optical discs are popular for music, movies, and software distribution due to their portability and durability. They can hold large amounts of data, with a standard CD storing about 700 MB, while a Blu-ray disc can hold up to 25 GB or more.