Filtering terminology

Parameters are filtering options that you add to a report to prompt the user to specify which data to display on the report at the time of viewing. You can create report parameters when you are designing the report in the Crystal Reports application, or you can override, modify, add new parameters, or add a custom parameter page to the report from the Reporting Services application.
See Parameters.
Reporting Services allows you to set up system-defined variables for use with parameters and schedules. Variables can be defined to simplify report generation for components that change regularly and across multiple reports. For example, you could define a variable called Current Period and assign a default value of Quarter 1. You can then add this variable to parameters on multiple schedules. You can then change the Current Period default value to Quarter 2, and any report schedules that use this variable will automatically use the Quarter 2 value.
Selection Formulas
A selection formula is a method of filtering the records or groups of records that are included at the time when you run or refresh a Crystal report. You can apply selection formulas when you are designing the report in the Crystal Reports application, or you can override, modify, or add new selection formulas to the report from Reporting Services.
Applying selection formulas decreases the report's processing time because when the report is run, the selection formulas filter out unwanted data, thereby producing a smaller report that contains only the necessary data. Also, this method creates reports that are customized for specific users or groups of users. You could create and deliver reports using selection formula an no parameters.
When you publish a Crystal report into Reporting Services, Reporting Services retains the selection formula information that you set up on the report. However, when you add or modify selection formula information, it saves the changes to the report that you published into Report Services, only. Reporting Services does not write any additions or modifications back to the original Crystal report file that reside outside of Reporting Services.
Note: See the Crystal Reports product documentation for more information about writing valid Crystal syntax. Reporting Services does not contain functionality to validate Crystal syntax.