Ad Hoc Reporting is a powerful feature of the report server which allows even unexperienced users to quickly create meaningful reports. As the operator of an server, you're able to specify the Ad Hoc layouts and datasources or dataviews available to the users as well as the appearance and features of the Ad Hoc user interfaces.
Depending on the choosed ad hoc layout the user can use the easy-to-use interface to set datasource, filter, grouping and data for chart or crosstab. If enabled in the ad hoc configuration the user can save the result as ad hoc report or rpt file.