Note: this filter type requires either SharePoint 2013 / 2010 (any edition, including Foundation), or Microsoft Office SharePoint Server 2007 (Enterprise Edition), with the Business Data Connectivity (BCS/BDC) features enabled in both scenarios.
Create a Business Data Connectivity (BCS/BDC) filter to send filters based on any data stored in any external data sources integrated into your Business Data Connectivity Service. Whether you let users pick an external data record or entity instance to use in interactive mode, or specify the record to use directly, the filter value being sent is always the current, live value from the specified data source.
To connect to your data source, first select the BDC external system and external content type type to use. Now you simply select which column values are displayed to users in interactive mode, and which column values are sent as filter values to connected Web Parts. You may also want to review any of the general filter settings that are naturally also available to your BDC filters.