In relationships it's the ability to address problems and deficiencies in a constructive manner. This includes picking up on things and expressing the necessary thoughts and emotions. People have different wavelengths when communicating.
It's far more complicated than just being forthcoming - or even "objective" - about problems, however.
Example: One of the last girls I dated asked me a loaded question about whether or not I really liked her as much as I claimed I did. I called her out for the question and told her of course I liked her. She wasn't happy about my bluntness.
The next day, I asked her if she wanted to talk more about the problem. I wanted to show good comminication skills by talking about it. She said no.
The day after that, I asked her if she had time for dinner that week. She told me she was busy.
Nothing happened day 3. On day 4 she sent me a message saying "I didn't think I wouldn't hear from you." She was expressing the fact that she felt used and/or neglected - as she had from the start.
Again, I bluntly pointed out that I had literally asked her to talk twice in one week and she had shot me down. So why am I getting grief from her?
I think I was being objective about the situation, but it begs the question: Was I communicating poorly by being too unsympathetic?
Whether she asked me a loaded question or not (I might be biased), did the fact that she brought up her problems show that she was being a good communicator? Possibly better than me and my possible lack of empathy?
We were on entirely different wavelengths and even though I might have been more direct communicator I wouldn't say it was "better" or even necessarily "good."