Quit
From Scriptwiki
Disconnects you from IRC and will give the optional message as the reason for your departure. (this message only appears to people who are on the same channels as you).
/QUIT [reason]
This commands sends a quit message to the server and waits until the server disconnects you.
Note that the reason will only be shown if chanmode +u isn't set.
See Also
To force a disconnect, take a look at /disconnect.
To connect to a server, use /server