Is there a name for "anti-convex" sets?

Question

Let $A \subset \mathbb{R}^n$. Suppose for all $x,y \in A$ with $x \not = y$, and for all $0 < t < 1$, we have $tx + (1-t)y \not \in A$. I like to say that $A$ is an "anti-convex" set. For instance, a sphere is anti-convex (I think?). Is there a former name for such a set property?