1. 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.
[French, 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 the Appendix of Indo-European roots.]
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