Great circle
From GeoWiki
A great circle is a circle on the surface of a sphere that has the same circumference as the sphere, dividing the sphere into two equal hemispheres. Equivalently, a great circle on a sphere is a circle on the sphere's surface whose center is the same as the center of the sphere. A great circle is the intersection of a sphere with a plane going through its center. A great circle is the largest circle that can be drawn on a given sphere.
Every circle formed by lines of longitude is a great circle - compare this to latitude where only the equitorial line of latitude is a Great Circle.
