Толковый словарь английского языка Oxford English Reference - apex

abbr. Association of Professional, Executive, Clerical, and Computer Staff. APEX n. (also APEX) (often attrib.) a system of reduced fares for scheduled airline flights when paid for before a certain period in advance of departure. Etymology: Advance Purchase Excursion APEX n. (pl. apexes or apices) 1 the highest point. 2 a climax; a high point of achievement etc. 3 the vertex of a triangle or cone. 4 a tip or pointed end. Etymology: L, = peak, tip