Answer
$y$ is a function of $x$.
Work Step by Step
Solve for $y$ in terms of $x$ to obtain:
$\begin{array}{ccc}
&\sqrt{y} - x &= &5
\\&\sqrt{y} &= &5+x
\end{array}$
Square both sides of the equation to obtain:
$\begin{array}{ccc}
\\&(\sqrt{y})^2 &= &(5+x)^2
\\&y &= &(5+x)^2
\end{array}$
The last equation above will give one value of $y$ for each value of $x$.
Thus, the equation represents $y$ as a function of $x$.