Answer
This is the slab of space between and including the planes $z=0$ and $z=6$.
Work Step by Step
This region is the set of all points $(x,y,z)$ that satisfy the equation $0 \leq z \leq 6$.
We know $z=0$ is the $xy$-plane, and $z=6$ is the plane that intersects the $z$-axis at the point $(0,0,6)$ and is parallel to the $xy$-plane. So since every point in our region has $z$-coordinate with $0\leq z \leq 6$, every point must lie in or between the planes $z=0$ and $z=6$.
Hence, our region is the slab of space between and including the planes $z=0$ and $z=6$.
