A pop-up window is a special type of overlapped window used for dialog boxes, message boxes, and other temporary windows that appear outside an application's main window. Title bars are optional for pop-up windows; otherwise, pop-up windows are the same as overlapped windows of the WS_OVERLAPPED style.
You create a pop-up window by specifying the WS_POPUP style in CreateWindowEx. To include a title bar, specify the WS_CAPTION style. Use the WS_POPUPWINDOW style to create a pop-up window that has a border and a window menu. The WS_CAPTION style must be combined with the WS_POPUPWINDOW style to make the window menu visible.