It is actually formed from the fusion of five vertebrae, and sits below L5, and above the coccyx. It is concave facing fowards, thus its curvature is considered a kyphosis[?].
The sacrum has dorsal and ventral foramina through which nerves can pass. Inferiorly, the sacral canal opens at the sacral hiatus.
wikipedia.org dumped 2003-03-17 with terodump