ICB stands for Internet Citizens Band. It's similar to IRC. You can find out about it on the ICB Home Page.
You can access ICB via your shell account with the command icb. To get a list of arguments accepted by icb, do:
icb -?
ICB help can also be found online (by typing /help) and in the directory:
/home/common/doc/icbThere you'll also find files called cicbrc.sample and sample.icbrc. You can cp cicbrc.sample to your home directory as .cicbrc to make icb more colorful. The file sample.icbrc demonstrates some of the ways that you can customize the behavior of icb.