(TRAVEL) [noun] [U], [adjective] [before noun] - abbreviation for Advance Purchase Excursion (= a system of cheap travel tickets which must be bought a particular number of days before travelling)an APEX fareIf you make a booking at least fourteen days in advance you can buy an Apex ticket which will be half the standard price.
APEX
Meaning of APEX in English
Cambridge English vocab. Кембриджский английский словарь. 2012