To begin, we need to understand the distinction between query and report parameters. A query parameter is passed to the data query engine to be incorporated into the SQL script's WHERE clause or some other part of the SQL that can accept parameters.
A report parameter is passed to the report processor to be processed while the report is rendered on the client. Both types of parameters are stored in the report definition (the RDL file), where you can manage them by using the Report namespace.
It's a useful exercise to examine the RDL (or RDLC) file to see how parameters are defined in the XML. Take a look at Figure 3—it shows a snippet of an RDL report definition that defines the report parameters. The Report Parameters dialog box that Figure 2 shows is used to define and (optionally) to set default, permissible values and other parameter attributes.