In F/OSS circles pre-Github a fork was when there was enough dissatisfaction with a F/OSS project (for many reasons) that people went through the effort of taking the source of a project at a given point and making an entirely new project based on it. Some famous examples of this kind of fork would be the GCC/EGCS fork, the Xemacs/Emacs fork, the DragonflyBSD/FreeBSD fork, the X.org/XFree86/Freedesktop multiway fork, the OpenOffice/LibreOffice fork, etc.

In this sense of the term “fork” it’s a major watershed event in F/OSS that sometimes shapes the way future projects run. (And sometimes, like the GCC/EGCS thing, one of the branches becomes the “new normal”.)

Post-Github, a fork is just what Github calls cloning a repository on their platform within their platform. Any time you look at a project on Github, if you have an account on Github you can “fork” it (in their sense of the term) which basically means you have a cloned snapshot of that project in your account. It’s functionally identical to typing "git clone " on your own machine only it’s all kept in Github’s own ecosystem.

What I find funny about the people protesting the second use as some kind of Github conspiracy is that the alternatives they themselves recommend instead … do exactly the same thing (but aren’t subject to the same conspiracy theorist tripe)! Cognitive dissonance is a HELL of a drug…