For an object moving in an elliptical orbit about another celestial body, the point of greatest separation is called the apoapsis (from the Greek apo = away from). At this point in the orbit, the object is travelling at its slowest speed (Kepler's Second Law).

The apoapsis is equivalent to the:

- Aphelion: for a celestial body orbiting the Sun,
- Apogee: for a celestial body (in particular the Moon or artificial satellites) orbiting the Earth,
- Apastron: for a celestial body orbiting a star (e.g. in a binary star system).

The point of closest approach in the orbit is called the periapsis.