Customize the Data Dictionary
You can hide available tables and fields in the data dictionary that you do not use in your reports.
This is helpful if you use only certain tables and fields in your reports and want to simplify the data dictionary to make it easier to select the tables and fields you use.
Note: Tables and fields created for custom objects can be viewed only in the All
Tables list in the report designer’s data dictionary. This prevents customizing the data
dictionary to display only custom object tables. See Overview of Custom Objects.