1) Periapsis 2) Periapsis in lunar orbit 3) Periselene 4) Point of periapsis 1) Periselene 
That point in a lunar orbit which is nearest to the Moon.
The point on an elliptical lunar orbit that is nearest to the Moon.
Periapsis in lunar orbit. 
The closest point to the Moon in an object's orbit around it.
perilune That point at which a spacecraft in lunar orbit is closest to the moon's center: applied especially if the spacecraft was launched from the moon.