Report Definition Language (Report Builder 1.0)
When you design your report layout in Report Builder, you are actually creating a report definition. Report definitions in Reporting Services are written in a programming language called Report Definition Language (RDL). A report definition contains information about the data source you selected, the fields that you added to your report, and the formatting information of the data and text boxes. When you save your report, you are storing the report as an .rdl file on the report server.