Jung's beginning work revolved around focus of energy. "Was it on the object (the external world)... or was it on the subject (the internal world)...?" The focus of energy is called the "attitude-Type" of a person. Jung thought it was biological and even exists in babies.
Those with a extroverted preference focus on the outer world/"object." Extroverts are "externally focused and driven." Little energy is left over for internal focus. They're often (not always??) energized by spending time around others and get bored or drained when they spend time alone. They tend to think out loud and discuss thoughts with others. Extroverts also tend to be verbally fluent. "What you see is what you get."
"Now, when orientation by the object predominates in such a way that decisions and actions are determined not by subjective views but by objective conditions, we speak of an extroverted attitude. When this is habitual, we speak of an extroverted type. If a man thinks, feels, acts and actually lives in a way that is directly correlated with the objective conditions and their commands, he is extroverted." - Jung, 1976
Introversion
"Although the introverted consciousness is naturally aware of external conditions, it selects the subjective determinants as the decisive ones. It is therefore oriented by the factor in perception and cognition which responds to the sense stimulus in accordance with the individual's subjective disposition." - Jung, 1976
Attitude Compensation