Functional disorder refers to a medical condition where an organ or body part appears normal but does not function correctly. This type of disorder often lacks visible symptoms, making it difficult to diagnose. A few synonyms for the term functional disorder include nonspecific functional syndrome, functional somatic syndrome, somatoform disorder, medically unexplained symptoms, and psychosomatic disorder. Somatoform disorder specifically refers to physical symptoms that cannot be explained by medical investigations and may potentially be linked to psychological distress. Medically unexplained symptoms and psychosomatic disorder both refer to physical symptoms that are believed to have emotional or psychological triggers. In contrast, non-specific functional syndrome and functional somatic syndrome are broader terms that encompass multiple types of functional disorders.