In the Force.com platform, the Report type is a set of rules that determine which records and fields appear in the report. The Report types are categorized into two;
Standard report types
Custom report types
Custom report types allow you to build a skeleton in the report wizard from which users can create and customize reports. With custom report types, you can enable users to create reports from the predefined objects, object relationships, and fields that you specify. You build custom report types of the relationships (master-detail and lookup) between objects so that you can:
Choose which standard and custom objects to display to users creating and customizing reports
Define the relationships between objects displayed to users creating and customizing reports
Select which objects' fields can be used as columns in reports
To create a custom report...