Definition of APEX fare:
Advance purchase excursion fare. International non-cancelable return airfare ticket offered at a heavy discount on the conditions that (1) the ticket is purchased and bookings for departures at either end are made at least 21 days in advance, (2) the minimum gap between departures is of one to six weeks (typically two weeks), (3) the maximum gap between departures is of 12 to 24 weeks (typically 16 weeks), and (4) there are no stopovers. Cancellation of an APEX fare trip usually results in higher than normal penalties.
Meaning of APEX fare & APEX fare Definition