We categorize the Task Status to show Due tasks (executable immediately and not dependent on others - i.e. waiting) - and Open tasks (not completed)

Task StatusDue TasksOpen TasksUse
Not Startedyesyes- Initial Status (1)
- Click on Reopen
- the prerequisite was completed (2)
In Progressyesyes
Completednono- Click on Complete
Waiting on someone elsenoyes- Task has a prerequisite (3)

custom status codesNot Closed and where status does not contain "Waiting" or "Deferred"Not Closed

You can overwrite the default Salesforce Task Status codes used in 

> Setup > Custom Metadata Types -- Checklist Settings: