0day means no patch is available, whether the vulnerability is known privately/publicly or not
I’m a fan of letting context infer meaning. And letting certain words just naturally grow to whatever the culture wants it to. It’s always hard to fight back against it.
There’s a million examples of this on the internet where people try to be pedantic about slang or word usage. All that matters is “we know what you mean”. I like to assume enough people here know the real difference zero days vs existing vulnerabilities are. But in practice it matters less.