You can create reports with parameters that the person viewing the report can adjust, which is easier than creating multiple reports with the same basic layout and similar data.
Simple parameterization involves changing data values. For instance, you might give readers an option to filter by the values in a drop-down list. This can include values stored in a particular column; for instance, you could choose to parameterize a column that contains product names, in which case the report reader would be able to change which product he wanted to see data for. Simple parameters are added after the data structure has been defined through a query.
Advanced parameters give readers the power to change the structure of the data. For instance, you might offer an option to select among multiple columns in a given table. These parameters must be expressed as formulas, and are executed along with the query.