INTJ is an abbreviation used in the publications of the Myers-Briggs Type Indicator to refer to one of the sixteen personality types. More at Wikipedia
Myers-Briggs Type Indicator - The Myers-Briggs Type Indicator assessment is a psychometric questionnaire designed to measure psychological preferences in how people perceive the world and make decisions.
Keirsey Temperament Sorter - The Keirsey Temperament Sorter is a self-assessed personality questionnaire designed to help people better understand themselves and others.
Rational temperament - The Rational temperament is one of the four temperaments defined by David Keirsey.
Mastermind (Role Variant) - The Mastermind Rational is one of the 16 role variants of the Keirsey Temperament Sorter, a self-assessed personality questionnaire designed to help people better understand themselves.