A 3-Dimensional ellipsoid is given by the equation:
$$\frac{x^2}{a^2} + \frac{y^2}{b^2} + \frac{z^2}{c^2} = 1$$
Let $a=20, b=15$ and $c=10$. Then as per my understanding, $a$ is the major axes and $c$ is the minor axes. What axes is $b$ called? I am confused. Please provide some references too.