Confidence comes not from knowing you know everything, but from knowing you can handle what comes up. - Donn King
Confidence is knowing what you are good at; knowing the value that you can provide to a situation; and the ability to convey this to others by way of speech, mannerisms and body language. Confidence also indicates that you are aware of your weaknesses and the ability to accept that your point of view may not be the only one around. [Let's not confuse confidence with arrogance]
Personally - I'm a confident person. I'm very comfortable with myself and my point of view on various topics; and I'm not afraid to ask questions or learn about the subject areas that are not my forte. Over the years I've learned that unless one is willing to take a risk - you'll never know what the outcome was (and that may leave some feelings of regret at some point in time). Just remember that nothing can substitute experience.
A simple example. If you're the kind of person who loves the idea of exploring new countries but can't find a have a travel companion - why not go traveling on your own ? The idea can seem daunting but think about all the people you will meet and all the places that you will see. Once you get the flight booking done - it's just about sorting out your accommodation; then heading over to TripAdvisor to check out places to visit; maybe join a social network where you plan to visit and meet a few people. Once you start setting small goals for yourself - everything falls in place. So just be confident. Life is about doing things now and not letting opportunities pass you by.
What about you ? How confident are you as an individual ? Have you ever felt a lack of self-confidence ? What did you do to overcome that ?