A clinical case definition, also known as a clinical definition or simply a case definition, is a list of clinical criteria used by public health professionals to determine whether a person's illness should be included as a case in an outbreak investigation—that is, whether a person should be considered directly affected by an outbreak. In the absence of an outbreak, case definitions are used in public health monitoring to classify the disorders that exist in a community. A case definition establishes boundaries for a case by limiting time, person, place, and shared definition of the phenomenon under investigation. All cases of a disease documented from a specific time period may be included in the time criteria.