grey area 
noun
An ill-defined situation or area of activity not readily conforming to a category or set of rules: grey areas in the legislation have still to be clarified...
- Furr isn't opposed to exploiting the gray areas in the NASCAR rule book - actually, that's half the challenge.
- There are indeed many grey areas within this issue, but I am quite sure that the law is correct in maintaining euthanasia's illegality.
- I used to be idealistic enough to think that all the world was clean and tidy, that rules were rules, that there were no gray areas anywhere.