The dark circle within the cone is an ellipse.
An example of an ellipse are the rings of Saturn.
Origin of ellipseModern Latin ellipsis ; from Classical Greek elleipsis, a defect, ellipse ; from elleipein, to fall short ; from en-, in + leipein, to leave (see loan): so named from falling short of a perfect circle
- A plane curve, especially:a. A conic section whose plane is not parallel to the axis, base, or generatrix of the intersected cone.b. The locus of points for which the sum of the distances from each point to two fixed points is equal.
Origin of ellipseFrench, from Latin ellīpsis, from Greek elleipsis, a falling short, ellipse, from elleipein, to fall short (from the relationship between the line joining the vertices of a conic and the line through the focus and parallel to the directrix of a conic) : en-, in; see en–2 + leipein, to leave; see leikw- in Indo-European roots.
(third-person singular simple present ellipses, present participle ellipsing, simple past and past participle ellipsed)
From French ellipse.