@Rosemary It's a musical release term, I think a holdover from vinyl record days. Distinguishing a single track release from a slightly larger collection of tracks, usually 4-5. The larger collection is still not a full album, so it's called Extended Play, or EP.
When there's a full album of songs (I would guess over 6 tracks or 60 minutes of playtime), it becomes a Long Play, or LP.

@emanate See, we'd thought LP just meant a type of record that could hold more recording.

@Rosemary Yeah. I think LP has just become synonymous with vinyl records, while "album" has crossed over to general use on any medium.
EP remains, for whatever reason, to mean a mini-album, much like "novella" is a word for a shorter-form novel.

@emanate Well, we'd thought of it as a specific type of vinyl record, that had completely replaced an earlier one, similar to how high-density 3½" floppy disks completely replaced the older ones.

@Rosemary Hmm, looking this up more, it's both.
https://en.m.wikipedia.org/wiki/LP_record

It was a format that became the standard for albums, which then mutated into being used as a shorthand for "album".

@emanate Analog audio recording technology is fascinating.