The window is similar to a page, you can add any widget to it and it has two configurations for displaying content: fixed and anchored. The fixed window creates a modal that disables the main window but keeps it visible so users can interact with the window before they can return to the experience. A fixed window can be used as a splash screen, opened with a page or from a widget. An anchored window is triggered from a widget such as a button or a text widget.
In the app config, the windows are defined by dialogs.