Wikipedia
The term Tritype refers to a theory regarding the Enneagram of Personality and was coined by Enneagram researcher and coach Katherine Chernick Fauvre. The word tritype was formed from Latin, with the prefix tri meaning three, and the word type added referring to the Enneagram types. The theory was initially inspired and developed as the result of research studies Fauvre conducted in 1994-1995 on the internal experience and personal image of the 9 types. Later, in 1996, Katherine met a teacher from Arica that referenced Oscar Ichazo's teachings on a similar theory that he referred to as the "tri-fix", but there was nothing published on Oscar Ichazo's "tri-fix" work. In December 1996 and January 1997, Enneagram Monthly published an interview with Oscar Ichazo that included the concept of tri-fix. This validated Fauvre's research findings that individuals have not just one, but 3 Enneagram types. In 2008, Fauvre coined the term Tritype in order to distinguish the Fauvres' vast research and resulting theory from both Ichazo’s teachings, as well as from the teachings of Arica.
Tritype theory suggests that while individuals primarily utilize one of the main Enneagram types as their "core type", everyone actually employs three central Enneagram types - the one that is the most dominant within each center of intelligence (the Head (567), Heart (234) and Gut (891) centers respectively). According to Katherine Fauvre, individuals use their main Enneagram type along with two other types in a consistent and cascading manner, to produce a kind of ego intersection among all three types. Therefore, while each type within the Tritype is employed separately, the combination of all three types coming together gives each Tritype a unique defense strategy (or way of defending against reality) and a focus of attention. The Tritype is used to explain the distinctive way in which each individual manages life using various combinations of ego strategies and coping mechanisms, yet Tritype (like the Enneagram) still remains a theory of motivation and not one of behavior.
Fauvre frequently refers to the "high side" and "low side" of these Tritype interactions and distinguish each as having a separate purpose. The high side of the Tritype intersection is that it gives direction, focus and purpose to the individual ego. The low side of this Tritype intersection is that it creates a blind spot which can narrow a person's ability to accurately self-assess and may even prevent a person from achieving a higher level of self-awareness by keeping them stuck in habitual and self-defeating patterns.