Many dictionaries translate it to "ambiguity",but it looks so indefinitely.
I'm looking for more expressive answer.
Depending on context, 暧昧[pronounced as ài mèi] can take on a few meanings. The following is quoted from Baidu with some explanations in English:
暧昧 is usually used to describe a kind of ambiguous relationship that is neither here nor there. It is not necessarily a negative word.
(someone1) flirt with (someone2). 玩暧昧，玩调情
暧昧 is a kind of relationship betweenwomen and men, it exists in friendship, but the degree is higher than friendship, it’s almost love but has not become love yet.
I don’t think there is a perfect English word which can perfectly express this meaning, actually we always can’t find a correct word which has exactly the same meaning in another language, so don’t worry about this.
Personally it is a "shady relationship", although I am not a local english speaker.
I'd say its similar to being flirtatious with someone, but it's more Chinese culture related.
Because Chinese culture puts emphasis on being indirect, the relationship between a men and women can be somewhat unclear. 暧昧 describes the relationship of two people between "friendship" and "partnership". Think of two people with mutual affection but haven't told each other their feelings. I know it is also common in western world but I would say it exists more in Chinese couples.
Common ways of 暧昧 use: When you see a guy and a girl are flirting with each other but they denied that they are in a relationship. You call that 暧昧.
It means the relationship of two people that you assume they are feeling affectionate towards each other.
To me, ambiguity is not right word for that.
I would change upon different circumstances. When it's about a state of relationship, I would say amorous ambiguity, but when it's an adjective I would say it's blurred, ambiguous, or unclear.