The commerce server is a new addition to the xSP solutions package as of version 10. It replaces the ACS component that was used in versions 6 and 7.
The Commerce Server is a web service with a graphical user interface which allows you to create a catalog of products to be offered to your customers. The NovaBACKUP client will connect to this web service to sign up for your backup service offerings. Through the Commerce Server the account will be provisioned on your backup server, and will record the billing information.