system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What makes a CD an EP and not an LP or album?
gpt
EP and LP are terms that originated with the technology of vinyl records.

An LP is a 12" vinyl record which when played at 33-1/3 rpm gave you ~22 minutes per side -- they were able to stretch that a little bit but not too much.

A 'single' was a 7" vinyl record with a bigger hole in the middle (it was developed by a different company who originally wanted to sell a different player) which when played at 45 rpm gave you a single song on each side of 3-5 minutes (later stretched when singles got longer).

An 'EP' was in the middle.  The format varied but often it was a 7" record but played at 33-1/3 RPM instead of 45 RPM so you could fit perhaps 10 minutes on each side.

In the industry, the format ceased to matter after a while, an EP became synonymous with a 3-6 song release.  Whenever a group is inspired enough to write more than a single and its B-side but not inspired enough to write a full album they could release something in the middle and call it an EP.