In order to fit experimental data, I want to use a Cartesian equation which looks like:

$\left|\dfrac{x}{a}\right|^{z} + \left|\dfrac{y}{b}\right|^{z} = 1$

$a$, $b$, $c$, and $z$ can take any real value, except the impossible ones ($a = 0$ or $b = 0$, for instance).

First, **I look for a name for this equation** because I can't find more information about it if I can't name it. As far as I know, ellipsoids, paraboloids, or hyperboloids are not helpful here, since with those specific cases, $z = 2$, and that's all.

Any idea? Thanks!