It is an unwanted half-boner. It isn't at the point of a full erection and isn't completely limp. You are on the fence and you are not sure which side of the fence you are going to land on. It may become a full erection or your penis may just fall back into dismay. You may get one from waking up in the morning, or the act of a chick possibly grinding on you.
-Do you have a boner
-No, I unfortunately have a half-boner
-Oh, you mean a jing wing.
-Man I have a jing wing right now.
-You do. Why?
-Well, that chick has been grinding on me for a while. I want to like her but all I'm getting is a jing wing.
-Maybe she isn't right for you.