Drill-In is when you navigate from one table to the next, filtered on a specific task.
An example of a drill-in will be:
If you click on a client in the Client table who has accounting switched on as a service.
Then go to the Accounting department and the Accounting table in the top navigation.
Click on the icon next to the table name.
You will be taken to the Accounting table filtered on all tasks for that client.
A Breadcrumb will appear in the top-right corner, indicating the path which you have navigated from.
You can click on any part of the Breadcrumb to be taken back to that table. In this example, clicking on Client in the Breadcrumb will take me back to the Client table.