Basic equation given by (z=x
2/a
2+y
2/b
2) where a and b are
constants.
Cross-sections of the graph parallel to the xy plane are ellipses and cross-sections parallel to the xz and yz planes are parabolas. It looks sort of like a bowl, only it extends to infinity rather than having a brim. This is a standard shape that people first learn in multivariable calculus and such when they actually care about formulas and equations of figures in more than two dimensions.