Refer to X11 'graphical applications'.

For people who know they need graphical applications but don't know what
X11 is.

doc/config.but

@@ -2892,8 +2892,8 @@ PuTTY in a variety of ways, such as \cw{true}/\cw{false},
 The X11 panel allows you to configure \i{forwarding of X11} over an
 SSH connection.
 
-If your server lets you run X Window System applications, X11
-forwarding allows you to securely give those applications access to
+If your server lets you run X Window System \i{graphical applications},
+X11 forwarding allows you to securely give those applications access to
 a local X display on your PC.
 
 To enable X11 forwarding, check the \q{Enable X11 forwarding} box.

doc/using.but

@@ -328,10 +328,10 @@ information.)
 \H{using-x-forwarding} Using \i{X11 forwarding} in SSH
 
 The SSH protocol has the ability to securely forward X Window System
-applications over your encrypted SSH connection, so that you can run
-an application on the SSH server machine and have it put its windows
-up on your local machine without sending any X network traffic in
-the clear.
+\i{graphical applications} over your encrypted SSH connection, so that
+you can run an application on the SSH server machine and have it put
+its windows up on your local machine without sending any X network
+traffic in the clear.
 
 In order to use this feature, you will need an X display server for
 your Windows machine, such as Cygwin/X, X-Win32, or Exceed. This will probably