An Excel trusted file location is a SharePoint document library, a UNC path, or an HTTP Web site that is configured as a trusted repository for workbooks that Excel Calculation Services can access. Excel Calculation Services opens workbooks that are stored in trusted file locations only.
If you are planning to use a new SharePoint document library as a trusted file location for Excel Services in Microsoft Office SharePoint Server 2007, create the new document library on a SharePoint site. To create the new document library, click the Site Actions menu, select Create, and then click Document Library. On the New page, type a name for the new document library and click Create.