What is Case type in Pega 7

A case type is a work class that inherits from Work–Cover– and contains a case type rule. A case type can cover or be covered by other case types. A case management structure can also include work classes that inherit from Work-. These work classes may be covered by case types, but cannot cover other work classes or case types. The covering relationships among case types are defined in case type rules. As a best practice, configure the case type structure in the Case Explorer.
When a case type work item (case) is created, the case is said to be instantiated.
 Be careful not to confuse a case with a case type, which is sometimes referred to as a case.
Work classes that inherit from Work– are commonly called work types.