Like the term "wellness", the term "holistic" also suffers from severe overuse. Almost every concept in culture and science, which has to do with the connection of two or more individual ideas, is called holistic, and it is indeed confusing, focus on “holistic management”, "holistic culture" and finally "holistic healing practice" to create an overview.
Of course, only a holistic understanding of the body is interesting for the concept of wellness, which is also represented in a strong way by the various schools of naturopaths in Germany.
Medical wellness is based to a large extent on this understanding of the body, which consists of body and soul, or possibly also from body, composed of spirit and soul.
The principle here is actually very simple: one assumes, that mental states or mental sensations have a strong influence on the physical condition of a person and tries, to treat various physical ailments at this root instead of restricting oneself to medical symptom control - hence the term "holistic".