irssi/docs/help/in/silence.in

@SYNTAX:silence@

Works only in some IRC networks.

SILENCE is similar in many respects to IGNORE, except that it is 
server-based. What this means is the server will never even send 
you messages from anyone you have silenced, whereas it will with
IGNORE, where your client is responsible for filtering the messages 
out. This has the advantage of not bogging your client down with 
excessive data as it tries to filter out messages. The silence list
is lost when you disconnect. SILENCE only affects private messages
and invites.

The default behavior is to SILENCE a nick!user@host pattern, and 
if such a pattern is not passed as the argument, it must be prepended 
with a plus ('+') to be added to your silence list. If a pattern is 
prepended with a minus ('-'), it will be removed from your silence list. 
If you only specify a nickname, you can list the patterns in the 
silence list owned by that nickname. If no arguments are given, your 
own silence list is displayed. 
 
See also: IGNORE, ACCEPT