Answer:

A Plane which passes through the center of a sphere intersects the sphere in a great circle.

For example, circle of longitude on a globe are great circles, but circles of latitude are not great circles (except for the equator).

Great circles are the largest circles which can be drawn on a sphere. Circles of latitude, apart from the equator, are not as large. The shortest distance between two points on a sphere is along the great circle passing through the points.

A great circle is the intersection of a sphere with a plane going through its center. A great circle can be demonstrated by tightly stretching a piece of sewing thread across the surface of a globe between the start and finish points of the intended journey. Great circles serve as the analog of straight lines in spherical geometry.