Definitions
1.nounThe point, in an orbit about the Earth, that is closest to the Earth: the periapsis of an Earth orbiter.
2.noun(more generally) The point, in an orbit about any planet, that is closest to the planet: the periapsis of any satellite.
3.noun(possibly obsolete outside astrology) The point, in any trajectory of an object in space, where it is closest to the Earth.