This code system http://hl7.org/fhir/request-priority defines the following codes:

Code Display Definition
routine Routine The request has normal priority.
urgent Urgent The request should be actioned promptly - higher priority than routine.
asap ASAP The request should be actioned as soon as possible - higher priority than urgent.
stat STAT The request should be actioned immediately - highest possible priority. E.g. an emergency.
<status value="draft"/> <experimental value="true"/> <date value="2022-05-28T12:47:40+10:00"/> <publisher value="HL7 (FHIR Project)"/> <contact> <telecom> <system value="url"/> <value value="http://hl7.org/fhir"/> </telecom> <telecom> <system value="email"/> <value value="fhir@lists.hl7.org"/> </telecom> </contact> <description value="Identifies the level of importance to be assigned to actioning the request."/> <caseSensitive value="true"/> <valueSet value="http://hl7.org/fhir/ValueSet/request-priority"/> <content value="complete"/> <concept> <code value="routine"/> <display value="Routine"/> <definition value="The request has normal priority."/> </concept> <concept> <code value="urgent"/> <display value="Urgent"/> <definition value="The request should be actioned promptly - higher priority than routine."/> </concept> <concept> <code value="asap"/> <display value="ASAP"/> <definition value="The request should be actioned as soon as possible - higher priority than urgent."/> </concept> <concept> <code value="stat"/> <display value="STAT"/> <definition value="The request should be actioned immediately - highest possible priority. E.g. an emergency."/> </concept> </CodeSystem>