Mononucleosis, commonly called mono, is an illness caused by the Epstein-Barr virus. Although it's rarely serious, mono can cause bothersome symptoms that last several weeks.
Complex systems. Complex systems present problems both in mathematical modelling and philosophical foundations. The study of complex systems is an approach to science that investigates how relationships between parts give rise to the collective behaviors of a system and how the system interacts and forms relationships with its environment.
Family Systems theorists pay careful attention to the boundaries between family members, because such boundaries are exactly where problems tend to manifest. A boundary is a sort of psychological perimeter and definition that people draw around themselves, and around particular relationships they are involved in.