Source:http://linkedlifedata.com/resource/umls/id/C1879547
NCI: To cause something to start or to stimulate activity.,HL7V3.0: <p><b>Description:</b>Change the status of an object representing an Act to "active", i.e., so it can be performed or is being performed, for the first time. (Contrast with REACTIVATE.) For an HL7 Act, the state transitions per the HL7 Reference Information Model.</p>,NCI: In biology, to stimulate a cell in a resting state to become active. This causes biochemical and functional changes in the activated cell.