BD = Business Decline. This indicates to the employee that there is no firm shift end time.
Here's an example to show how BD works in 7shifts:
In this case, you are scheduling an Employee from 5pm-BD.
From their perspective, they are working at 5pm and will be sent home when things slow down, with no specified end time.
Admin / Manager Perspective:
Since 10pm is entered as the shift's end time, you will get an approximate labor cost for this shift (5 hours).
Don't worry, the shift end time is not visible to the Employee.