Answer
This is the half space lying in front of and including the plane $x=-3$.
Work Step by Step
This region is the set of all points $(x,y,z)$ that satisfy the equation $x\geq -3$. So this is the set of all points with $x$-coordinate greater than or equal to -3.
We know $x=-3$ is the plane that intersects the $x$-axis at $x=-3$ and is parallel to the $yz$-plane. So since every point in our region has $x$-coordinate greater than or equal to -3, every point must lie in front of the plane $x=-3$.
So our region is the half space lying in front of and including the plane $x=-3$.
