Source:http://linkedlifedata.com/resource/umls/id/C1550501
HL7V3.0: <p>The principle target on which the action happens.</p><p><i>Examples:</i>The patient in physical examination, a specimen in a lab observation. May also be a patient's family member (teaching) or a device or room (cleaning, disinfecting, housekeeping).</p><p><i>UsageNotes:</i>Not all direct targets are subjects. Consumables and devices used as tools for an act are not subjects. However, a device may be a subject of a maintenance action.</p>