Under UNIX, if the DISPLAY environment variable is set then GNU emacs
will create a window to run in. Otherwise it will run as if on a terminal,
in which case it will need to be told what type of terminal it is.
This is normally done automatically, at login time, but if it
is not you must describe the terminal in a terminal capability
database such as terminfo or TERMCAP.
Refer to your UNIX documentation for a description of this facility.