Essential parts are the components that make up a whole. PITHS, cores, hearts, and VITALS are all essential parts of something. PITHS are the innermost layer of a plant stem, core is the central or innermost part of something, heart is the most important or essential part of something, and VITALS are the essential organs of the body. All of these terms refer to essential parts of something, whether it be a plant, an object, or a person.