The purpose of language is to communicate an idea. All words are made up / all are equally valid. Some are more made up than others, sure, but if communication happens, it’s just as valid as any other.
Aside: there are technically two competing schools of thought on this, prescriptivism (language *must* work this way) and descriptivism (*this is how people seem to be using this word*). Prescriptivists get made when people use literally to mean figuratively; descriptivies say “ooh, interesting, people are using ‘Trespass’ as a transitive verb? Time to update the dictionaries, I guess!” (aside: every major dictionary describes itself as descriptivist. So the excuse of “that’s not what the dictionary says” is sort of like arguing that you can’t be grilling an egg on the hood of your car because the thermometer says it’s only 68. The egg still sizzles!)
Language works on a shared understanding. New words get created for precision. Jargon is a specific word (or way of using an existing word) that exists to create clarity in a specific context (usually industry). Friend groups have their own jargon !
But here’s the thing: no word truly has a rigid, fixed context. Take Friday. 5th day of the week1. Goes between Thursday2 and Saturday. Seems pretty rigid!
Except the phrase “It’s my Friday” is immediately understood by all: sure it’s Tuesday, but I don’t have to labor for the next day or two.
That’s how you get definition 2: the last day before a work-week ends.
I don’t think you’ll find that definition in any modern dictionary, but the usage is there, and the meaning is understood.
Words aren’t special. Go make up your own. Maybe they’ll even catch on.