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

CodeDisplayDefinition
routine RoutineThe request has normal priority.
urgent UrgentThe request should be actioned promptly - higher priority than routine.
asap ASAPThe request should be actioned as soon as possible - higher priority than urgent.
stat STATThe 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>