From Longman Dictionary of Contemporary Englishellipseel‧lipse /ɪˈlɪps/ noun [countable] CFa curved shape like a circle, but with two slightly longer and flatter sides → ovalExamples from the Corpus

ellipse• Whereas in an ellipse m + n constant, in a hyperbola m - n constant.• A circle will knit as a circle not an ellipse, a square, a square not a rectangle and so one.• A circle is multi-fold, whereas an ellipse has two-fold symmetry.• The drawing elements of the program are vector-based, and concentrate on shapes, including boxes, polygons and ellipses.• Folding of square, pentagon, ellipse, spider and tetrahedron.• The circle is a special case of the ellipse in which the two axes are equal in length.• Indeed, model-interpretive anaphors, unlike ellipses, do not require linguistic antecedents at all.