Region

"Region" is a simulated environment as itself (or simulated parameters). It's not quite same meanings to sim, but many peoples misunderstood so. The land in SL is hosted on a Linux server , each CPU handle 65,536 m² (256x256m) region. Current class5 host server has 4 CPU cores, so each server handle 4 regions. (except for void type region which are 4 per CPU).

To learn more about the servers hosting SL, you can read the series of articles [1] that have been posted to the SL blog.

See: Viewer coordinate frames