Pseudoscience alert!
Despite its popularity, MBTI has no scientific basis and MBTI tests are very inconsistent across retests, even though MBTI claims that a person’s personality supposedly remains the same throughout their life. It is also under criticism for rigidly categorizing people under distinct categories, even though personalities can be extremely nuanced.
The Myers-Briggs Type Indicator is personality inventory based on questionnaires to identify preferences in how people perceive the world and make decisions. It is based on cognitive functions and divides the population into 16 personalities. These 16 personalities are distinguished based on their preferences in each of the four axes: Introverted vs Extroverted, iNtuiting vs Sensing, Thinking vs Feeling, and Judging vs Perceiving. MBTI claims to help the test-taker become aware of their personality and path of development. In particular, the test-taker can use their own function stack to realize their strengths and work on their weaknesses. Unfortunately, MBTI tests, when repeatedly taken, often do not yield the same result. Test results can change in a matter of months or even weeks, which is one of the major reasons MBTI is considered pseudoscientific. That is not to say MBTI cannot be a useful tool (see also this post)