Revolutions Per Minute (RPM) is a frequency unit, used to measure rotation speed.
Vinyl records we manufacture can be played at 331/3 RPM or 45 RPM.
While 331/3 RPM allows for longer playing times, 45 RPM allows for higher sound quality.
331/3 RPM is sometimes (incorrectly) abbreviated as just 33 RPM.
- Wikipedia article on RPM: http://en.wikipedia.org/wiki/Revolutions_per_minute