A smooth oval shape created by stretching a circle; in geometry, the set of points where the sum of distances to two fixed points is constant.
From Greek 'elleipsis' (deficiency, falling short), because an ellipse is a 'deficient circle' (one that falls short of being perfectly round). Adopted into English mathematics terminology in the 17th century.
The word 'ellipse' literally means 'falling short'—ancient Greeks named it this because they thought of it as a circle that failed to be round, but actually ellipses are everywhere in nature: planetary orbits, ripples in water, even your pupils when you look at them sideways!
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