A dialog box is a special kind of menu for asking you a yes-or-no question or some other special question. Many Emacs commands use a dialog box to ask a yes-or-no question, if you used the mouse to invoke the command that led to the question.
To disable the use of dialog boxes, change the variable
nil. In that case, Emacs always
performs yes-or-no prompts using the echo area and keyboard input.
This variable also controls whether to use file selection windows (but
those are not supported on all platforms).
A file selection window is a special kind of dialog box for asking for file names. You can customize the variable use-file-dialog to suppress the use of file selection windows, even if you still want other kinds of dialogs. This variable has no effect if you have suppressed all dialog boxes with the variable use-dialog-box.
When Emacs is compiled with GTK+ support, it uses the GTK+ file
chooser dialog. Emacs adds an additional toggle button to this
dialog, which you can use to enable or disable the display of hidden
files (files starting with a dot) in that dialog. If you want this
toggle to be activated by default, change the variable
x-gtk-show-hidden-files to t. In addition, Emacs adds
help text to the GTK+ file chooser dialog; to disable this help text,
change the variable x-gtk-file-dialog-help-text to