Contributed By: Cliff Hobbs [MVP SMS]
Reproduced from the Microsoft Software Update Services: Frequently Asked Questions web page:

"Microsoft Software Update Services is a no-charge add-in component for Windows 2000 and Windows Server™ 2003 that is designed to greatly simplify the process of keeping computers in your organization up to date with the latest critical updates, security updates, and service packs.

SUS installs a web-based application that enables administrators to quickly and reliably deploy updates to desktop and server machines running Windows 2000, Windows XP, and Windows Server 2003. The updates can be synchronized from the live Windows Update servers and saved on the SUS server. Then, after approving only the updates you have tested and want to distribute, they can be downloaded from the SUS server by the Automatic Updates component on client machines."