unscheduled debt: A debt that should have been listed by the debtor in the schedules filed with the court but was not. (Depending on the circumstances, an unscheduled debt may or may not be discharged.)
It's a bad idea to try to hide assets. If the court finds out you failed to list something on your schedule, and finds that you hid it intentionally, they will deny a discharge under §724(a)(4)