I think it might be referring to the Desktop Manager set up CD. When you install Desktop Manager, it gives you 3 options, BES (Corporate Server), Redirector, and BIS (Personal).
With Redirector, you have to have the PC up and running to get email. With BIS, you set up the BB and your email accounts on your carrier"s BIS site and your email is pushed to you automatically. BES requires the corporate email server.