Answer
Interaction function.
Work Step by Step
$g(x,y,z) = \frac{xz-3yz+z^2y}{4z}$
As $z\ne 0$ we can divide the numerator by $4z$. This gives us:
$g(x,y,z)=\frac{x-3y+zy}{4}$
One of the terms has the product of two variables in it ($\frac{+zy}{4}$), therefore it is an interaction function.
