This is the very top of the "Description" section of the Wikipedia page for "Grey-zone (international relations)"[0]:
> Use of the term grey-zone is widespread in national security circles, but there is no universal agreement on the definition of grey-zone, or even whether it is a useful term, with views about the term ranging from "faddish" or "vague", to "useful" or "brilliant"
It goes on to say:
> Grey zone warfare generally means a middle, unclear space that exists between direct conflict and peace in international relations.
[0] https://en.wikipedia.org/wiki/Grey-zone_(international_relat...