The perihelion is the point in the solar orbit of a planet, comet, or other object when it is nearest to the Sun. The perihelion distance is the distance between the object and the Sun at this point. The time of perihelion passage is the time at which an object is at perihelion.
Argument of perihelion
The argument of perihelion is the angle between the ascending node and the perihelion of an orbit around the Sun, measured in the orbital plane and in the direction of orbital motion. It specifies the direction of the major axis of an orbit around the Sun and is one of the orbital elements.