Important: The most current version of the Report Design Wizard does not contain this step. See Post Wizard Steps in the following document http://wiki.pentaho.org/display/Reporting/3a.+Report+Wizard+%28version+1.8+or+higher%29.
This step is valid for reports that are being created from a template only. When using a template report you must provide the wizard with values for certain labels that may appear in the report. Templates also have custom headers/footers that reference certain columns from the query. Since the template cannot assign a column name; you must provide that mapping in this step.
In the sample above, you are setting the Report_Title Mapping Key to the Product Line Report.
There are three different types of mappings. A label mapping is a straight text replacement used for display purposes only. An item or detail mapping is used to map a column that appears in the items section of the report. A group mapping is used to setup report groups. When the report groups are mapped, the wizard automatically updates the report to use the desired columns as groups.