Many tasks don't have due dates—you just need to wash the car sometime, for example. Nevertheless, you can optionally assign a due date and/or schedule a reminder for any task. (Due dates and reminders are independent of one another. A task can have a due date, a reminder, both, or neither.)
A due date specifies when a task must be completed. Unlike an appointment, a due date is associated only with a date, not a time.