Elongation

Elongation is a term applied to Mercury and Venus.

When seen from Earth, the two inferior planets appear to become closer or further away from the Sun as they move round their orbits. When either planet reaches its greatest angular distance from the Sun, they are said to have reached eastern (or western) elongation.

Elongation is not a fixed point in their orbits as it is an observational factor that depends on where the Earth is in its orbit as well as the position of Mercury and Venus in theirs.