A physical entity which is the primary unit of operational and/or administrative interest in a study. For example, a person who is registered in a study as a recipient of an investigational product or as a control. May also include individuals who are being screened for studies, or individuals participating in observational or other studies. Other examples may include a devicess such as a pacemaker or a fuse that can be used in medical devices, a cow, a farm, a pen of pigs, a tissue sample from a tissue bank, etc. Note that the subject might not be an entire entity but a part of one, for exaample, a patch of person's skin where dermatological products are tested. The one person may have multiple areas of skin being tested simultaneously for different products - in this case, each area of skin would be a separate research subject. Note also that study subjects within a study are all of the same type. "A physical entity which is the primary unit of operational and/or administrative interest in a study." - HL7 FHIR, ResearchSubject