A gramophone record (phonograph record in American English) or vinyl record, commonly known as a "record", is an analog sound storage medium in the form of a flat polyvinyl chloride (previously shellac) disc with an inscribed, modulated spiral groove. The groove usually starts near the periphery and ends near the center of the disc. Phonograph records are generally described by their diameter in inches (12", 10", 7"), the rotational speed in rpm at which they are played (, , 45, 78), and their time capacity resulting from a combination of those parameters (LP – long playing rpm, SP – 78 rpm single, EP – 12-inch single or extended play, 33 or 45 rpm); their reproductive quality or level of fidelity (high-fidelity, orthophonic, full-range, etc.), and the number of audio channels provided (mono, stereo, quad, etc.).