Aphelion refers to the point farthest from the sun in the orbit of a planet or other celestial body.
For the planet Kwejian, this was one of the orbital characteristics listed in its catalog. The aphelion for the planet was 0.728213 au, or 108,939,000 kilometers. (DIS: "The Sanctuary")
The aphelion of planets in the Chin'toka system was listed in a computer graphic display viewed by Benjamin Sisko. The graphic indicated that the aphelion was 109 km. (DS9: "Tears of the Prophets")