What is the slope of the line that passes through the points $(-1,-2)$ and $(-1,-3) ?$

Step 1 ：The slope of a line passing through two points $(x_1, y_1)$ and $(x_2, y_2)$ can be calculated using the formula $\frac{y_2 - y_1}{x_2 - x_1}$.

Step 2 ：In this case, the x-coordinates of both points are the same, which means the line is vertical.

Step 3 ：The slope of a vertical line is undefined.

Step 4 ：Therefore, the slope of the line that passes through the points $(-1,-2)$ and $(-1,-3)$ is undefined.

Step 5 ：Final Answer: The slope is \(\boxed{\text{undefined}}\).