The highest point.
The point, in any trajectory of an object in space, where it is farthest from the Earth.
The point, in an orbit about the Earth, that is farthest from the Earth: the apoapsis of an Earth orbiter.
The point, in an orbit about any planet, that is farthest from the planet: the apoapsis of any satellite.
The highest, ultimate point of achievement which can be reached; perfection.
A prohibition against proceeding further; an insuperable obstacle or limiting condition.
The perfect or most extreme example of its kind; the ultimate.