What do you call two variables that if one of them is non-zero, the other is always 0 and vice-versa

Question

Let's say I have two variables x and y. If x is non-zero, then y must be zero. Similarly, if y is non-zero, then x must be zero

I'm writing a dissertation (in electronics) and I'm wondering if there's a technically correct way of saying the above perhaps using some neat mathematics?

Apologies if this is off-topic, I googled for it but couldn't find much.

Thanks.