Perihelion was the point nearest the sun in the orbit of a planet or other celestial body.
A story told by a hologram of Doctor Stephen Hawking, he stated that "in that frame of reference, the perihelion of Mercury would have precessed in the opposite direction." Data further explained that "the joke depends on an understanding of the relativistic curvature of space-time. If two non-inertial reference frames are in relative motion…" but he was abruptly interrupted by Sir Isaac Newton. (TNG: "Descent")
The perihelion of planets in the Chin'toka system was listed in a computer graphic display viewed by Benjamin Sisko. The graphic indicated that the perihelion was 107 km. (DS9: "Tears of the Prophets")
For the planet Kwejian, this was one of the orbital characteristics listed in its catalog. The perihelion for the planet was 0.718440 au, or 107,477,000 kilometers. (DIS: "The Sanctuary")