What do you call for approximations having a characteristic "Z" / really-sharp curve to it?

Question

It's called a Sigmoid/logistic curve for an "S" shaped curve of a mathematical function. What's the name for a "Z" or a sharp counter-part to it or is there no name for such?

Answer 1

Nvm, found it. It's called a [Hard-Sigmoid][1]

[1]: https://en.wikipedia.org/wiki/Hard_sigmoid. Examples include; Piecewise linear function

Answer 2

A step function. That's actually a bit broader. The Heaviside step function $$H(x) = \begin{cases} 0 & \textrm{if } x < 0 \\ 1 & \textrm{otherwise} \end{cases}$$ is more specific.