The LP (from “long playing” or “long play”) is an analog sound storage medium, a phonograph record format characterized by: a speed of 33+1⁄3 rpm; a 12- or 10-inch (30- or 25-cm) diameter; use of the “microgroove” groove specification; and a vinyl (a copolymer of vinyl chloride acetate) composition disk. Introduced by Columbia in 1948, it was soon adopted as a new standard by the entire record industry. Apart from a few relatively minor refinements and the important later addition of stereophonic sound, it remained the standard format for record albums (during a period in popular music known as the album era) until its gradual replacement from the 1980s to the early 2000s, first by cassettes, then by compact discs, and finally by digital music distribution.