Does anyone know the equation of an oval, i.e. a planar egg-shaped curve? I need y=f(x) or the parametric form x=f1(t), y=f2(t) or even the equation in polar coordinates r=f(theta), thata being the polar angle.

I don't care if its axis of symmetry is the x or the y (or any other) axis, nor the position of the coordinate system origin relative to the curve.