Answer
$x =a \cos \theta; y=a \sin \theta$ and $z=Z$
Work Step by Step
Let us consider $Z$ be the axis parameter and the radial parameters can be written as: $\sin \theta$ and $\cos \theta$.
Here, $\theta \in [0, 2\pi]$ and $0 \leq Z \leq h$ and $h$ is the height of a cylinder.
Thus, the parametric description for a cylinder with radius $a$ can be expressed as:
$x =a \cos \theta; y=a \sin \theta$ and $z=Z$