Intranet--- An intranet is a private computer network that uses Internet protocols, network connectivity to securely share part of an organization's information or operations with its employees. Sometimes the term refers only to the most visible service, the internal website. The same concepts and technologies of the Internet such as clients and servers running on the Internet protocol suite are used to build an intranet. HTTP and other Internet protocols are commonly used as well, FTP.There is often an attempt to use Internet technologies to provide new interfaces with corporate 'legacy' data and information systems.

Briefly, an intranet can be understood as "a private version of the Internet," or as a version of the internet confined to an organization
internet--- The Internet is a worldwide, publicly accessible network of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP). It is a "network of networks" that consist ...more

The answer given by ramsurya serves the purpose.
intranet can be understood as "a private version of the Internet," or as a version of the internet confined to an organization while the Internet is a worldwide, publicly accessible network of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP).

The Internet is an open, public space, while an intranet is designed to be a private space. An intranet may be accessible from the Internet, but as a rule it's protected by a password and accessible only to employees or other authorized users.

"Intranet" is in-house netwroking with features of internet like mail, chat, sharing..etc