\begin{definition}[Definition:Diameter of Ellipse/Also defined as]
Some sources define the '''diameter''' of an ellipse $\KK$ as a chord of $\KK$ which passes through the center of $\KK$.
This is a perfectly adequate definition of a '''diameter of an ellipse'''.
However, the definition does not work so well in the context of:
:a hyperbola, as it does not encompass diameters which are not chords
:a parabola, which does not have a center.
\end{definition}