All Modular Merchant documentation uses the phrase Administration Area, when referring to the shopping cart software's control panel. The phrase "backend" is not actually used within the software or its documentation.

The Administration Area is the part of your Modular Merchant store which only your store Admins see, and includes all of the System Settings, the product and category organization, the modules, and the reports.

Your customers never see the Administration Area; they only see the storefront.