Name of function which similar to characteristic function.

Question

The characteristic function of subset $A$ of set $X$ is defined by \begin{align*} I_A(x)= \begin{cases} 1&x\in A\\ 0&x\not\in A \end{cases}. \end{align*}

What the name function which defined by \begin{align*} \ldots_A(x)= \begin{cases} 1&x\not\in A\\ 0&x\in A \end{cases} ? \end{align*} (which similar to characteristic functions)