@SYNTAX:wall@

This command sends a message to all operators in a channel. If the server
supports WALLCHOPS or STATUSMSG=@, it sends a notice to @#channel.
Otherwise it sends a notice separately to each operator, which may not
be a very good idea to use in a channel with lots of operators.

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

See also: WALLCHOPS