Finding the volume using double integrals

Find the volume of the wedge sliced from the cylinder ${x}^{2}+{y}^{2}=1$ by the planes $z=a(2-x)$ and $z=a(x-2)$.

I am confused because ${x}^{2}+{y}^{2}=1$ is a unit circle not a cylinder. and the other two are lines in the zx plane where $y=0$. I don't see how they are planes, are they planes or are they just lines in the zx plane (when $y=0$).

Find the volume of the wedge sliced from the cylinder ${x}^{2}+{y}^{2}=1$ by the planes $z=a(2-x)$ and $z=a(x-2)$.

I am confused because ${x}^{2}+{y}^{2}=1$ is a unit circle not a cylinder. and the other two are lines in the zx plane where $y=0$. I don't see how they are planes, are they planes or are they just lines in the zx plane (when $y=0$).