ESTJ (Extraversion, Sensing, Thinking, Judging) is an acronym used in the Myers-Briggs Type Indicator (MBTI) publications to refer to one of the sixteen personality types. The MBTI assessment was developed from the work of prominent psychiatrist Carl G. Jung in his book Psychological Types, which proposed a psychological typology based on his theories of cognitive functions.
From Jung's work, others developed psychological typologies. Well-known personality tests are the MBTI assessment, developed by Isabel Briggs Myers and Katharine Cook Briggs, and the Keirsey Temperament Sorter, developed by David Keirsey. Keirsey referred to ESTJs as Supervisors, one of the four types belonging to the temperament he called the Guardian.
The dominant Extraverted Thinking (Te) means ESTJs use logical fact-based judgments in the outer world of people and actions. This again explains their behavior and leadership qualities. The auxiliary Introverted Sensing (Si; concrete perception in the inner world of thoughts and feelings) is connected with memory or familiarity, and thus is what leads them to defend the status quo and procedures. Extraverted iNtuition (Ne) is using abstract perception in the outer world, and gives them the ability to conceptualize. However, this is subservient to the inward concrete focus. Last, the Introverted Feeling is a value-based judgment used in the inner world of thoughts and feelings. This is associated with connection or kinship to other people when values or beliefs are "congruent", and hence is the ESTJ's weakest link.