KILL is used to forcibly remote a client from the irc network. It works similarly to KICK, except that a reason must be given (even if it is meaningless or flat-out wrong).
In general, KILL is useful only as a warning tool for abusive users. Modern irc clients (this one included) have automated means for reconnecting to a server after a disconnection (whether due to a KILL or something else), so KILL is by no means a permanent solution. It is not intended as a means for personal vendettas; this practice is generally frowned upon.
