Creatures that can interact with the world have essenses: Body, Mind, and Soul.
Is a character muscle-bound, insightful, brilliant, charming, nimble, or hardy? Essences define these qualities—a creature’s assets as well as weaknesses.
The four main rolls of the game: the Essence Roll, the Skill Roll, the Defense Roll, and the Attack Roll, rely on The Three Essence Scores. Each of these rolls use the essense to add or subtract using a modifer on a d20.