Answer
Hyperbollic paraboloid.
Work Step by Step
The form of the equation is
$\displaystyle \frac{y^{2}}{1^{2}}-\frac{x^{2}}{1^{2}}=\frac{z}{1},\quad $
which is a Hyperbollic paraboloid (when comparing to Table 12.1).
The cross sections with planes $x=k , y=k$ are parabolas,
and the cross section with planes $z=k$ are hyperbolas.
