irssi/docs/help/in/wall.in

@SYNTAX:wall@

This command sends a message to all operators in a channel. This is internal
irssi command which sends a message separately to each opearator, so this
may not be very good idea to use in channel with lots of operators.

Some IRC servers support also /MSG @#channel or /WALLCHOPS which you should
use if possible.

See also: WALLCHOPS