Answer
This is the plane that intersects the $x$-axis at $x=5$ and is parallel to $yz$-plane.
Work Step by Step
This region is the set of all points $(x,y,z)$ that satisfy the equation $x=5$. So this is the set of all points with $x$-coordinate equal to 5.
We know the $yz$-plane is the set of all points $(x,y,z)$ with zero $x$-coordinate, so we can obtain our region by shifting each point in the the $yz$-plane 5 units in the positive $x$-direction.
Hence our region is the plane that intersects the $x$-axis at $x=5$ and is parallel to $yz$-plane.