What does apex mean?
The definition of apex
A”pex, n.; pl. E. Apexes; L. Apices.
Etym: [L.]

1 The tip, top, point, or angular summit of anything; as, the apex of a mountain, spire, or cone; the apex, or tip, of a leaf.
2 (Mining)
The end or edge of a vein nearest the surface. [U.S.] Apex of the earth’s motion (Astron.), that point of the heavens toward which the earth is moving in its orbit.