What does it mean for an activation function to be "saturated/non-saturated"?
Please see this answer.

An activation function is considered non-satured if

$$
\lim_{z \rightarrow \infty} f(z) = \infty
$$

A saturated activation function has a compact range such as $[-1,1]$ for $\tanh$ or $[0,1]$ for the sigmoid.