the point on the celestial sphere toward which the sun and solar system appear to be moving relative to the fixed stars
"The ancient astronomers believed that the apex was the direction in which our solar system travels through space."
The highest or the greatest part of something, especially forming a point.
"The airline announced that its new Apex fares are available only to members who book their flights at least three months in advance."
The highest point in a plane or solid figure, relative to a base line or plane.
Acronym of advance purchase excursion (an air fare)
In plain English: Apex means the very top, highest point, or peak of something.
"The mountain climbers reached the apex of their journey when they stood at the very top of the peak."
Usage: Use apex to describe the literal peak of a geometric shape or the figurative summit of an organization's success. Avoid using it for general tops unless you specifically mean the sharpest or most prominent high point.
Acronym of Association of Professional, Executive, Clerical and Computer Staff.
"The staff members at APEX met weekly to discuss workplace policies under their union's new leadership."
The word comes from the Latin apex, which originally meant "point," "tip," or "summit."