Long-playing Definition

lôngplāĭng, lŏng-
adjective
Designating or of a phonograph record having microgrooves, for playing at 3313 revolutions per minute.
Webster's New World

Referring to records that recorded a greater amount of sound than previous versions had, an LP, generally a 12 inch 33 1/3 RPM record.

Wiktionary
Synonyms:
  • long-play