0⁰

I have always assumed that $0^0$ is undefined with the same «severity» as $0 \div 0$, but in a lot of contexts, it is actually defined as $0^0 = 1$.
Most notably to me in this category are the IEEE floating-point numbers 1.

1

There is technically the powr function, which treats $0^0$ as NaN, but most programming languages use the pow function.