Here's what that means:

* Not perfectly circular: While often depicted as circular, planetary orbits are actually slightly oval-shaped.

* Sun at one focus: The sun is located at one of the two focal points of the ellipse. This means that the distance between a planet and the sun varies throughout its orbit.

* Perihelion and Aphelion: The point in a planet's orbit where it is closest to the sun is called perihelion, and the point furthest from the sun is called aphelion.

It's important to note that while the orbits are elliptical, they are very close to being circular. This is why they are often represented as circles for simplicity.