Only one of the subforms from within the subform set is rendered based on conditions specified by the form author.
The object is visible on-screen, visible in the printed form, and occupies space in the form layout. Visible is the default presence setting for all objects.
The object is visible on-screen, not visible in the printed form when printed from within Acrobat or Adobe Reader, and occupies space in the form layout.
The object is not visible on-screen, visible in the printed form (when printed from within Acrobat, Adobe Reader, or directly from the server), and occupies space in the form layout.
The object is printed when using double-sided printing. This option is useful when you want to place the page number in a different corner of the page when using double-sided printing than when using single-sided printing.
See also 

Subform set properties in the Subform Set tab