Hi Chris.
A crossfire bridge is a cable that connects two crossfir graphics cards so that you can produce a "nearly twice as good" graphics card.
For details of crossfire, see:
http://ati.amd.com/technology/crossfire/faq.html
For the bridge, see:
http://www.tigerdirect.com/applications/searchtools/item-Details.asp?EdpNo=2918988&sku=H231-7186
http://content.guru3d.com/newsitem.php?id=4015