Biholomorphically equivalent domains

Definition

Let $U,V\subset {\mathbb{C}}^n$ be domains (open connected subset). We say that $U,V$ are biholomorphically equivalent if there exists a holomorphic function $\phi :U\to V$ with a holomorphic inverse ${\phi }^{-1}:V\to U$.

(By a holomorphic function from $U$ to $V$, we mean a holomorphic function from $U$ to ${\mathbb{C}}^n$, whose image lies completely inside $V$. In this case, we get a bijection from $U$ to $V$ that is holomorphic both ways.