Quick Definition: The calmness and confidence one instills when he or she has developed the skills necessary to have good sex, and to acquire good sex when the need arises.
The parallels between what makes good sex and a good pickup are quite similar. In bed, being dominant, being immersed in the process, and having a sense of humor are all key tools to having good sex. Similarly, picking up a girl also has many of these elements in place.
A guy who has options when it comes to sex does not beg or otherwise betray his true value when he meets new girls. Because he has options, he is confident around beautiful women. He knows the feeling of being sexually dominant over her and exerts a sense of control because he knows that only he can give her that level of satisfaction in bed. Conversely, a guy who is not good in bed often suffers because he cannot keep the girl, and adds yet another reason for not being confident when talking to women.
Watch Hugh Hefner answer the questions in true sexual confidence @4:50:
True sexual confidence comes from the knowledge of knowing what women want sexually.