Tying "fork" to "repositories" is nonsense, because software forks have existed longer thsn e.g. git.
How do you define "repository", such that it makes sense? Is it only Git repositories? Any version control system? How about a .zip-file placed on an FTP server?
Can you fix dictionary.com as well?
Computers. to copy the source code from (a piece of software) and develop a new version independently, resulting in two unique pieces of software
Thst's not at all how it works. The definitions made in the TOS do not "leak" out of said TOS (unless the TOS specifies that, which it does not).
So you also agree that copying is not forking as it is commonly understood?
Do you then claim that the license refers ro "fork" as defined in a specific service's TOS (without referencing said servixe at all)?
Otherwise I don't see how you can come to the conclusion that "forking" in the license does not also necessify modification (which is what the common meaning is).
An article exactly about how Github misuses the word "fork": https://drewdevault.com/2019/05/24/What-is-a-fork.html
How about you continue reading a bit further, until you hit the word "and".
take a copy of source code from one software package and start independent development
(emphasis mine).
Github defines "forking" as just copying, while normally it is understood as copying + further development (creating a "fork" in the development history, hence the name).
I edited my reply to include the definition from Wikipedia, but there are of course many other sources.
I got it from the TOS:
By setting your repositories to be viewed publicly, you agree to allow others to view and "fork" your repositories (this means that others may make their own copies of Content from your repositories in repositories they control).
They explicitly define it as making copies. There is no mention of being allowed to modify said copy. Also note the quotes around "fork", since it differs from the usual definition.
E.g. wikpedia (https://en.m.wikipedia.org/wiki/Fork_(software_development) defines it thusly:
In software engineering, a project fork happens when developers take a copy of source code from one software package and start independent development on it, creating a distinct and separate piece of software.
(Emphasis mine)
The TOS actually does not say you are granting users permissions to fork in the usually understood sense. The TOS gives you permission to copy, which Github calls "forking" even though it isn't.
Just because you can do something, does not mean you are allowed to.
The point is, it's not at all clear, because Github has it's own definition of what "fork" means. I'm honestly not sure why it's so hard to grasp.