Thomas Shey
Legend
I have decided that rule zero is nonsensical jargon of the worst order. Waffle is already taken, so I think it’s best dubbed as “trad pancake”.
I'm going to get into this a bit because, while I understand where you're coming from (in that its often thought to point to something more concrete and spelled out than is the reality), I think its possible to be too dismissive of the real phenomenon that term has become attached to.
First, it absolutely is a term that is sometimes used in game; its become well enough known that game designers will use it as header for the phenomenon without probably thinking about it.
That said, while its a term that appears to have been invented by the D&D 3e designers, it represented a set of expectations that had been epidemic in the D&D sphere (and sprawled out from there to some extent in other games the way all kinds of things from D&D did to one degree or another). Frankly, I don't have much sign that for most of the life of the game system it was not assumed to be the default in the general culture of D&D players. That didn't mean it was universal, but it was so much assumed that even challenging that assumption was often treated as a moral failing.
So while its origin is not as clearcut as it could be, its a term who's meaning and the expectations go with it are about as common as any general-use term in the hobby is, and people are absolutely representing a common game culture (and sometime overt rules advice) phenomenon when talking about it and the implications in the wild.