Variable: icon-title-format
icon-title-format is a variable defined in xdisp.c.
Value
(multiple-frames "%b" ("" "%b - GNU Emacs at " system-name))
Documentation
Template for displaying the title bar of an iconified frame.
(Assuming the window manager supports this feature.)
If the value is a string, it should have the same structure
as mode-line-format (which see), and is used only on frames
for which no explicit name has been set (see modify-frame-parameters).
If the value is t, that means use frame-title-format for
iconified frames.
Probably introduced at or before Emacs version 19.29.
Source Code
// Defined in /usr/src/emacs/src/xdisp.c
DEFVAR_LISP ("icon-title-format", Vicon_title_format,
doc: /* Template for displaying the title bar of an iconified frame.
\(Assuming the window manager supports this feature.)