Is forking a well defined term? Doubt it will hold up in court.

They don't give permission, so the lack of definition doesn't really matter.

If they were trying to grant a narrow permission and then enjoin someone they thought was outside of their definition, it would matter (But they just aren't giving permission to distribute modified versions).

Anything the owners of the Winamp code can find in order to take legal action on will be distributed. Rule 2 (and 3) is always superfluous in practice.

You can't have a private Github fork

Yes you can; it's set at the organization level

https://docs.github.com/en/organizations/managing-organizati...

I stand corrected

You can, but only private forks of a private repo are allowed. Private forks of public repos are not allowed by design (modulo some weird bugs that were discussed on a past post).