Domains report: The Domains report lists the organizations and Internet service providers your visitors use to browse your site. Examples of these organizations include comcast.com, verizon.com, and aol.com. These companies offer services that users subscribe to so they can access the Internet. It is part of Visitor Profile reporting.
Referring Domains report: The Referring Domains report shows the domains that referred visitors to your site. Use it to determine which external sites contribute the most to traffic and conversion metrics. It is part of Traffic Sources reporting.