Originally Posted by wikipedia.org

Introversion and extroversion

In the extroverted attitude the energy flow is outward, and the preferred focus is on people and things. Extraverts tend to be energetic, enthusiastic, action-oriented, talkative, and assertive. Therefore an extroverted person is likely to enjoy time spent with people and find less reward in time spent alone.

In the introverted attitude the energy flow is inward, and the preferred focus is on thoughts and ideas. Introverts tend to be quiet, low-key, deliberate, and disengaged from the social world. Thus, one who is introverted is more likely to spend time alone or in contemplation, as these activities are rewarding. They may avoid social situations entirely, not because of shyness, but because they choose to.