A number is assigned showing the degree to which each trait is present, and a four-letter acronym can be made of each of the 16 permutations -- the person's "type." Type does not change significantly over the course of years.
Engineers and software developers are split about 50/50 between INTP and ENTP, with fewer than 5% in other types. This is one explanation of the inherent bias in online communities.
The test is copyrighted and scoring is protected by trade secret. Motivated people have reverse-engineered it by comparing answer sheets to scores, though no free versions are publicly available.
The MBTI is highly regarded in pop psychology and group dynamics, where its simplicity makes it suitable. More comprehensive personality assessment tools, such as the Minnesota Multiphasic Personality Inventory (MMPI) are now more common in a clinical setting.
The recent communication course I went on had extrovert/introvert on one axis and task/people on the other. Curious whether this purported task focus vs people focus split is analogous to one of the Meyers-Briggs axis?
Similar two and three axis tests are fairly widespread. Some of the 16 MBTI types are fairly rare in the general population, and distinctions between some of them are relatively minor. Though I think "task focus" vs "people focus" is to a greater extent a cultural or environmental phenomenon rather than being organic.