A work field is a user-defined non-interface field for use by the service. You can think of work fields as an extension of a screen or COMMAREA. Work fields persist across operations, so the contents of the Work Fields pane in the Interface Mapper is the same for all operations of your service interface.
For example, to use data from one screen on another screen, in one operation you can assign the field containing that data to a work field. In another operation, you can assign that work field to a field on another screen.
Work fields can be alphanumeric or numeric. For all fields, you must specify a length and optionally the number of times the field occurs. For numeric fields, you can also specify the number of decimal places and whether or not the field is signed.