This code system http://hl7.org/fhir/appointmentstatus defines the following codes:

CodeDisplayDefinition
proposedProposedNone of the participant(s) have finalized their acceptance of the appointment request, and the start/end time may not be set yet.
pendingPendingSome or all of the participant(s) have not finalized their acceptance of the appointment request.
bookedBookedAll participant(s) have been considered and the appointment is confirmed to go ahead at the date/times specified.
arrivedArrivedSome of the patients have arrived.
fulfilledFulfilledThis appointment has completed and may have resulted in an encounter.
cancelledCancelledThe appointment has been cancelled.
noshowNo ShowSome or all of the participant(s) have not/did not appear for the appointment (usually the patient).
entered-in-errorEntered in errorThis instance should not have been part of this patient's medical record.