No whispering
Select the No whispering check box to disable the ability to whisper to one or more members within a channel.

A whisper is a private message that a channel member can send to one or more members of the same channel. To whisper, a member uses the IRCX WHISPER command and specifies each recipient by nickname.

A whisper is similar to the message a channel member sends using the IRC PRIVMSG command.