What does smooth hypersurface mean in $\mathbb{P}^2 \times \mathbb{P}^2$?

Question

Let $F \in \mathbb{C}[x_0, x_1, x_2, y_0, y_1, y_2]$. Suppose $F$ is homogeneous in both $x$ variables and $y$ variables. I see that $F = 0$ defines a hyper surface in $\mathbb{P}^2 \times \mathbb{P}^2$. What does it mean when this is a smooth hypersurface mean? Thank you.