This is a backronym. /usr is the original user home directory location on classic unix.

https://www.bell-labs.com/usr/dmr/www/notes.html

TIL after so many years that /usr isn't an abbreviation of "user". "UNIX/user system resources" makes a lot more sense in retrospect. Guess I should have RTFM a long time ago!

It looks like that's a newer interpretation than the original:

> As such, some people may now refer to this directory as meaning 'User System Resources' and not 'user' as was originally intended.

https://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/usr.htm...