...as opposed to "zero"? I know there's "Aleph null", "null set", and the German "null" for "zero", but where else is "null" used?
Do you mean in math, or in computing?
Both, though more importantly the former.
Well, I've seen "null transformation" when you're collecting ways to transform, e.g., a Rubik's Cube. That's all that leaps to mind in math.
In programming, "null" basically means zero, although it's usually used to describe a pointer that doesn't point to anything.
The C NULL pointer?
Yes.
Also there's null in JS, which is a value that you use when you intentionally want to set a variable to nothing (unlike undefined)