What is the general name for a surface of form $z = f(x, y)$? Is there a generic, geometrical name for a "sheet" of data, where the data fits the form: 
$$z = f(x, y)$$
Note that $z$ might be an actual third dimension (such as elevation in terrain data) or any scalar measurement (such as surface temperature).
I know you could generically say "it is a surface"... but a sphere or a cube also are surfaces, and I want to exclude them (from the term I'm looking for) because they are not single-valued in $f(x, y)$.
Note I'm not trying to get too picky that the surface is continuous in $(x, y)$ or discrete.  The dataset might be infinite in range, or only exist for some constrained region in $(x, y)$.  And I'm not concerned if the surface is continuously differentiable.  I'm looking for the term that glosses over all those.
I realize this is might just be called "planar data".  And in some contexts (e.g. terrain maps in video games) I think this may be called "two-and-a-half dimensional data".
But is there a well-established term in geometry or topology for this?
Thanks!
UPDATE:
I finally stumbled across the term I was looking for: "scalar field".  Perhaps this term is more common in physics than math; since my application is in the physical sciences (terrain elevation and radio propagation measurements) I'm probably going to use that in my work.
I really appreciate all who replied.
 A: A map of the form
$$\left(\begin{array}{c}
x\\
y
\end{array}\right)
\longmapsto
\left(\begin{array}{c}
x\\
y\\
z
\end{array}\right)
$$
where $z=f(x,y)$, which allows a parameterization of the surface
determined by the graph of the function $f$, is called Monge's chart.
It is needed that this map be injective and differentiable with domain an open set of $\Bbb R^2$. 
A: Given any function $F : X \to Y$, the set $$\operatorname{graph}(f) := \{(x, F(x)) : x \in X\} \subseteq X \times Y$$
is called the graph of $F$. (Sometimes this is denoted $\Gamma(F)$.) In particular, if $\Omega \subseteq \Bbb R^2$ and $f$ is a function $\Omega \to \Bbb R$, then we can identify $\operatorname{graph}(f)$ with $$\{(x, y, z) : (x, y) \in \Omega, z = f(x, y)\} \subset \Bbb R^3 .$$
The term graph is not specific to geometry or topology, but note that if $X$ and $Y$ are topological spaces, we can ask whether a function $F: X \to Y$ is continuous; either way, $\operatorname{graph}(F)$ inherits a natural topology, namely the subspace topology induced by the product topology on $X \times Y$.
A: Non-parametric or graph form are two commonly employed words.
