Marc,
That is the Due Date or Deadline of each particular workflow task, when you enable deadlines on your tasks. You can have some tasks with deadlines, and some tasks without deadlines.
A few cautions ... Windchill's functionality is a little weak in this area. It doesn't take into account working hours. So if the deadline is 3 hours, and the user receives a workflow task at 4:00 PM, it will be overdue at 7:00 PM.
