Definitions

Internet
a worldwide network of computers that allows the "sharing" or "networking" of information at remote sites from other academic institutions, research institutes, private companies, government agencies, and individuals

Intranet
An intranet is a private network that is contained within an organization that uses computers

Extranet
Group of Websites, each with a different owner, that joined together to share information; often used in supply chain management.

Local area network
Communications network connecting computers by wire, cable, or fiber optics link. Usually serves parts of an organization located close to one another, generally in the same building or within 2 miles of one another. Allows users to share software, hardware and data

Wide area network
WANs are networks that span the distance between buildings, cities and even countries. WANs are LANs connected together using wide area network services from telecommunications carriers and typically use technologies such as standard phone lines (called POTS (Plain Old Telephone Service) or PSTN
Metropolitan network
Telecommunications network which is used to connect particular locations to a backbone network