The Constant Editor is used to add constants to project items such as Windows, Web Pages, Views, classes and modules. Choose Constant from the command bar for the project item to add a constant. In the Inspector you can specify the name of the constant, its default value, type and scope.
In addition a String or Text constant can be made "localizable" which is a localized string whose value can changed based on OS or language.
Adding Constants, Localization topics