An application is a method of saving the DBU screens, files & fields the way a user has designed them.
After bringing up a file, selecting a logical, selecting & formatting fields, etc., type in APP in the control field of the initial DBU screen & a DBU application screen will appear. Press F6 to name & save your application.
This application can be accessed by typing the DBU command with DBUTYP(*DBUAPP) & giving the application name. You may also access an application by keying DBUAPP (App Name) and pressing Enter.