Hypoellipse

$$y^{n/m}+c\left\vert{x\over a}\right\vert^{n/m}-c=0,$$

with $n/m<2$. If $n/m>2$, the curve is a Hyperellipse.

See also Ellipse, Hyperellipse, Superellipse

References

von Seggern, D. CRC Standard Curves and Surfaces. Boca Raton, FL: CRC Press, p. 82, 1993.