Synset

the ambiguous region between two categories or states or conditions (usually containing some features of both)
<noun.attribute>

no man's land

twilight zone

sample sentences

"but there is still a twilight zone, the tantalizing occurrences that are probably noise but might possibly be a signal"
"in the twilight zone between humor and vulgarity"
"in that no man's land between negotiation and aggression"