In astronomy, when a body orbits the Sun, the shape of its orbit can be a circle or an ellipse. If the orbit is a circle, the Sun lies at the center of the circle and the distance of the body from the Sun is always a constant.
If the orbit is an ellipse, the Sun lies the focus of ellipse. As the body orbits the Sun, its distance from the Sun is not constant. The point at which it is closest to the Sun is known as perihelion and the point where it is farthest from the Sun is known as the aphelion.
The perihelion and the aphelion lie at opposite ends of the line segment passing through these points and the Sun. A body orbiting the Sun does not have multiple perihelion and aphelion points.
Another point to note is that only bodies orbiting the Sun have an aphelion and a perihelion in their orbit, these points for other bodies are known as apogee and perigee.