Eccentricity of a conic
= Eccentricity of a conic
{title2=$e$}
The parameter $e\geq0$ in a focus-centred <polar coordinates> equation $r=\ell/(1-e\cos\theta)$ for a <conic section>. It distinguishes an <ellipse> ($e<1$), a <parabola> ($e=1$), and a <hyperbola> ($e>1$).