A pop-up menu bar is one that is not normally visible. Instead, it pops up over the top line of the screen when the user activates it. The advantage of using a pop-up menu bar is that you have the full screen available to your program. The disadvantage is that the user cannot see the menu bar unless it has been activated (popped up). Pop-up menu bars are often used on character-based systems to conserve space.
You specify which type of menu bar you want by calling W$MENU with the WMENU-SET-CONFIGURATION parameter. (W$MENU is described in Appendix I of the ACUCOBOL-GT Appendices manual). Then, when the menu bar is displayed with the WMENU-SHOW parameter, your preferred menu bar type is used.