A GREY AREA means something that is not clearly defined and needs careful judgement.
“We have always had a professional attitude to copyrighted texts, but online copyright is still a bit of a grey area.”
Many people think they know what right and wrong are, but on closer examination it’s usually a grey area.
“It’s a grey area isn’t it?” (Meaning the speaker is talking about an unsure concept).
“I do well in math and most sciences, but chemistry is still kind of a grey area.”