Charisma - Having a compelling charm that inspires devotion in others.

You can be broke, unintelligent, foolish, and physically unattractive and still be successful if you have the ability to make other people genuinely want to help you.
Charismatic people are easy to recognize, they're the ones you can't help but like. They make other people feel good about themselves, are always present in the moment in your conversation, and have an uncanny ability to inspire trust. These people are popular because they're so good at making friends.

An Engineer I used to work with had an uncanny ability to make people like him and in so doing multiply his overall effectiveness. While my technical skills dwarfed his, he was still more valuable to the company than myself due to his ability to please people without kissing ass.

With a smile and 5 minute conversation he improved company morale, inspired others to work harder, communicated ideas effectively, and schmoozed customers into doing more business with us. He would remember the names of your family members and ask you about them in a non-weird way and actually care about your answers. I could definitely see him beating me for a job if we were to compete, and I'd be OK with that because I like the guy. That's the power of charisma.

I want to be clear that having genuine charm is not the same as being manipulative. One of my long time friends is a born salesman. He sells cars for a living and can convince people to trade in ol' reliable for a shiny new Cadillac and a mountain of debt when they had only intended on using the dealership parking lot to turn around. It's entertaining to spend time with him and observe his methods of getting what he wants in life by selling others on ideas.

But because he uses people to his advantage, the amount of trust anyone has for him is limited. His success is always cursed to be short term. Repeat business is low and he can't get to some people because they can immediately recognize false charm. To them, my friend is as obvious as the Cheshire cat, whose superficial smile seems to say 'I want you to trust me so I can betray you'.

Edit Sept 2015: I am not claiming that having charisma is valuable to society, only that it is valuable to the individual.