Technically, what we call uppercase letters are termed "majuscule" and lowercase letters are termed "minuscule". Since common manual movable type typesetting stations usually kept the more frequently used type in a case closer to the user, and the less frequently used type in a different case at a higher level farther from the user, the terms upper case and lower case came into common usage.
This reminded me - if anyone here has not seen "Linotype: The Film", it's a fantastic documentary and well worth watching. If Lauren's post was interesting to you, you'll like the film.
@cazabon There's a bunch of interesting Linotype stuff on YT. I have a Linotype maintenance manual. It is -- long.