grey area

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic An area intermediate between two mutually exclusive states or categories, where the border between the two is fuzzy.
• noun idiomatic A topic that is not clearly one thing or the other, that is open to interpretation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an intermediate area; a topic that is not clearly one thing or the other