Whereas the logo is the initial face of the company the corporate identity is it’s visual personality.
The identity normally starts with the logo, then the complete range of communication material should be designed to be consistent and follow the same guidelines so when someone sees a piece of literature or press ad they will recognise it to be from that company. The same guidelines should apply to on-line communication as well to include websites, email sends etc.
For some companies we will produce corporate identity guidelines, which cover every piece of communication material so anybody, including printers and other designers, can follow the guidelines so the company retains its identity.
And the reason for an identity? So that the company builds up a visual awareness, after all there is no point having a brochure, website, leaflet etc if they all look different, that's a waste of money.