display-graphic-p

display-graphic-p is a compiled Lisp function in `frame.el'.

(display-graphic-p &optional DISPLAY)

Return non-nil if DISPLAY is a graphic display.
Graphical displays are those which are capable of displaying several
frames and several different fonts at once. This is true for displays
that use a window system such as X, and false for text-only terminals.
DISPLAY can be a display name, a frame, or nil (meaning the selected
frame's display).