Answer
Hyperbollic paraboloid.
See image:
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Work Step by Step
The form of the equation is
$\displaystyle \frac{y^{2}}{1^{2}}-\frac{x^{2}}{1^{2}}=\frac{z}{1},\quad$
this is a Hyperbollic paraboloid (when comparing to Table 11.1).
The cross-sections with planes $x=k, y=k$ are parabolas; the cross-section with planes $z=k$ are hyperbolas.
