Introverts are not necessarily shy. Shy people are anxious or frightened or self-excoriating in social settings; introverts generally are not. Introverts are also not misanthropic, though some of us do go along with Sartre as far as to say "Hell is other people at breakfast." Rather, introverts are people who find other people tiring.
Extroverts are energized by people, and wilt or fade when alone. They often seem bored by themselves, in both senses of the expression. Leave an extrovert alone for two minutes and he will reach for his cell phone. In contrast, after an hour or two of being socially "on," we introverts need to turn off and recharge.
I never really understood before because my job often requires me to be very social and because I'm not really very shy, but I am totally an introvert. Pretty interesting article. You can read it in its entirety
here.