According to Carl G. Jung’s theory of psychological types, people can be characterized by their preference of general attitude:
Extraverted (E) vs. Introverted (I),
their preference of one of the two functions of perception:
Sensing (S) vs. Intuition (N),
and their preference of one of the two functions of judging:
Thinking (T) vs. Feeling (F)
The first criterion, Extraversion – Introversion, shows the source and direction of a person’s energy expression. An extrovert is usually full of energy expression. He/she likes to be in the external world, while an introvert tends to be in his/her world; they like to spend time with themselves.
The second criterion, Sensing – Intuition, represents the way someone perceives information. Sensing means that the person mostly believes information received directly from the external world. Intuition means that the individual believes mainly information provided from the internal or imaginative world.
The third criterion, Thinking – Feeling, represents how a person processes information. Thinking means that the individual takes the time to think before making a decision, they usually use logic to decide. Feeling means that the person usually makes a decision based on emotion; they make a decision based on what they feel rather than logic.
The fourth criterion, Judging – Perceiving, represents how the person performs information he or she has processed. Judging means that a person organizes all the events of life and, as a rule, sticks to his plans. Perceiving means that the individual is inclined to improvise, explore alternative options rather than following the particular plans.
Based on these four criterions, people take a test, which shows their combination of four letters, such as ISTJ, ESFP, INTP, ESTJ and other ten combinations. This combination of four letters shows the personality of the individual. From my own perspective, I can say that the test is very accurate, so if you want to take the test, here’s the link http://www.humanmetrics.com/cgi-win/jtypes2.asp