Many columns contain drop-down data lists that contain pre-defined values from which you can select a valid value for the column. Some values are created in definition tables, while others are defined in a table (Table Detail) that stores values from many different columns.
If the value is stored in Table Detail, Maintenance Screen is one of the options in the right-click menu for the column. When you choose Maintenance Screen, the Maintain Table Values window appears. In this window, you can add, delete, insert, or restore rows.