In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs (observed by someone other than the patient), symptoms (reported by the patient), phenomena or characteristics that often occur together, so that the presence of one or more features alerts the healthcare provider to the possible presence of the others. In recent decades, the term has been used outside medicine to refer to a combination of phenomena seen in association. Some syndromes, such as Down syndrome, have only one cause; others, such as Parkinsonian syndrome, have multiple possible causes. In other cases, the cause of the syndrome is unknown. The term syndrome derives from the Greek.