set display [on|off|toggle]
When turned off, this setting will cause the client to suppress all messages from being displayed (though it can still act on them internally. However, ECHO can still be used to explicitly print messages to the display.
This setting is automatically turned off while a script file is being loaded, including the .ircrc file. It is turned on again when the file finishes loading. This can be overridden by explicitly setting DISPLAY on inside the loaded scripts.