Abbreviation for Long Playing record (a.k.a. the record album). LP was a trademark of the Columbia Broadcasting Company, designating the then-new microgroove long playing record. The term was rapidly taken as a generic to distinguish the microgroove 33 1/3 RPM record from the standard 78 RPM records. The term became technically obsolete with the demise of the 78 RPM record, but lived on as a generic name for long playing record albums. Obviously the term is even more obsolete now that albums have been replaced by the Compact Disk format. LP records rarely contained more than about 45 or 50 minutes of music (as compared to the 60 – 70 minute times of many CD’s), and often had much less. Many of the terms and principles in dealing with audio today are vestigial remnants of producing music in an era where the final distribution was on vinyl records. Making records then was an art form that required audio to be manipulated in ways that would be unheard of in modern CD production.
(And yes, I still have a collection of records and a turntable that works.)