a grey area an ill-defined situation or field not readily conforming to a category or to an existing set of rules.
☞ In the 1960s, grey areas in British planning vocabulary referred to places that were not in as desperate a state as slums but which were in decline and in need of rebuilding.
2001Rough Guide to Travel Health In theory, it should be a cinch to diagnose appendicitis, but in practice it's much more of a grey area.