The Myers-Briggs Type Indicator is one of the most popular and widely used personality tests. Developed sixty years ago by Katharine Briggs and her daughter Isabel Briggs Myers, this tests measures fundamental differences in the way we make decisions, process information, and relate to the world. You've probably heard someone say, "I'm an ESTP and ISTJ" or something similar. What does this mean? Each letter signifies an important facet of personality.
E versus I
This scale measures Extraversion versus Introversion. Simply put, extroverts get their energy from the outside world and being with others, while introverts need time alone to refuel. Many people mistake this scale to be "outgoing" versus "shy." This is not the case. While introverts may appear shy, they may also seem quite gregarious. The difference is that an introvert will need time on her own to build up her energy before jumping into the world again.
S versus N
Signifying Sensing versus Intuition, this scale measures how you take in information about the world. A Sensor is concrete, seeing details and what is actually present. Most people are sensors. Intuitives, on the other hand, see possibilities. Sensors and Intuitives living together often clash in this respect; Sensors feel it is more important to take care of details like cleaning and paying bills on time, while Intuitives are more interested in starting new and exciting projects and endeavors than taking care of mundane tasks.
T versus F
The only scale with a clear gender bias, this measures whether we make decisions based on Thinking or Feeling. Whether because of some innate difference or our cultural training, men are more likely to fall into the category of Thinkers, who value logic and reason in their decision-making, while women are more likely to use personal and moral values and consider the feelings of all involved when they make a decision. This is by no means an absolute, though; a significant percentage of women are Thinkers, and vice versa.
J versus P
Another scale that describes decision-making, this signifies Judging versus Perceiving. You'll get a start on understanding this scale if you ask yourself, "Am I more comfortable before a decision is made or after?" A Judger like to have things settled and planned. A Perceiver likes to feel that there are still many options.