An extranet is a private network that uses Internet protocols, network connectivity, and possibly the public telecommunication system to securely share part of a business's information or operations with suppliers, vendors, partners, customers or other businesses. An extranet can be viewed as part of a company's Intranet that is extended to users outside the company (eg: normally over the Internet). It has also been described as a"state of mind" in which the Internet is perceived as a way to do business with other companies as well as to sell products to customers.

An argument has been made that"extranet" is just a buzzword for describing what institutions have been doing for decades, that is, interconnecting to each other to create private networks for sharing information.