glutSetWindowTitle man page
glutSetWindowTitle — Request changing the title of the current window
OpenGLUT - window
glutSetWindowTitle(const char* title);
New window title
glutSetWindowTitle() requests that the window system change the title of the window.
Normally a window system displays a title for every top-level window in the system. The initial title is set when you call glutCreateWindow(). By means of this function you can set the titles for your top-level OpenGLUT windows.
Some window systems do not provide titles for windows, in which case this function may have no useful effect.
Because the effect may be delayed or lost, you should not count on the effect of this function. However, it can be a nice touch to use the window title bar for a one-line status bar in some cases. Use discretion.
If you just want one title for the window over the window's entire life, you should set it when you open the window with glutCreateWindow().
Only for managed, onscreen, top-level windows.
Not all window systems display titles.
May be ignored or delayed by window manager.