What does EP mean
and
What does LP mean in musical terms ??

These were originally terms from the days of vinyl. "Long Playing" was at one time a CBS trademark, when the first 12" vinyl records playing at 33 RPM and using a diamond stylus were created, around 1940. Prior to that, most recordings were released on 10" hard rubber disks which played at 78 RPM, used steel needles, and had poor fidelity and lots of surface noise. They were capable of recording 5-6 minutes of music per side of the disc.

Originally the LP format was capable of about 18 minutes per side. That was designed so that one movement of a typical symphony could be recorded on a side, making it possible to release a symphony in a two-disc package and with the breaks occurring only between movements, as opposed to the 78 format which took 5-6 discs and had to have breaks in the middle of movements.

When the 45 RPM format became the format for popular music in the '50s, some people were dissatisfied because at first they could only record about 3 minutes per side. So various mutant formats termed "EP" began to appear, so that some popular and experimental music pieces could beat the 3-minute limit. Some of these were just LP-format disks that didn't use all of space available -- they might have 1-2 tracks with about 10 minutes per side (and a huge runout area). Other EP formats consisted of 12" disks that played at 45 RPM, or 10" vinyl disks that played at 16 or 33 RPM. These formats pretty much disappeared during the '70s, but made a brief comeback in the '80s just before CDs took over.

Nowdays, in the CD era, people tend to use the term "EP" to describe any CD that contains less than what is usually considered a full disc -- 60 minutes or so.