A pseudo-top-level domain is a label or name for a computer network that is not participating in the world-wide official

Domain Name System The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned t ...

and may not even participate in the Internet, but may use a similar domain name hierarchy. Historically the best known large networks in this group were

.bitnet BITNET was a co-operative U.S. university computer network founded in 1981 by Ira Fuchs at the City University of New York (CUNY) and Greydon Freeman at Yale University. The first network link was between CUNY and Yale. The name BITNET original ...

.csnet The Computer Science Network (CSNET) was a computer network that began operation in 1981 in the United States. Its purpose was to extend networking benefits, for computer science departments at academic and research institutions that could not be di ...

.oz MHSnet is a store-and-forward Message Handling System for wide area networks. MHSnet and its precursor, SUN3, were used to implement the Australian Computer Science network, commonly known as ACSnet, which connected Australia's Universities to each ...

, and

.uucp UUCP is an acronym of Unix-to-Unix Copy. The term generally refers to a suite of computer programs and communications protocol, protocols allowing remote execution of commands and transfer of Computer file, files, email and netnews between compute ...

, for which many Internet mail forwarders provided connectivity. In addition, newer networks like

.exit .onion is a special-use top level domain name designating an anonymous onion service, which was formerly known as a "hidden service", reachable via the Tor network. Such addresses are not actual DNS names, and the .onion TLD is not in the Int ...

.i2p The Invisible Internet Project (I2P) is an anonymous network layer (implemented as a mix network) that allows for censorship-resistant, peer-to-peer communication. Anonymous connections are achieved by encrypting the user's traffic (by using ...

, may be included. (Newest draft of the proposal expired on July 28, 2015 without becoming a standard.) Some domains such as

.onion .onion is a special-use top level domain name designating an anonymous onion service, which was formerly known as a "hidden service", reachable via the Tor network. Such addresses are not actual DNS names, and the .onion TLD is not in the I ...

later become officially recognised. Although these networks or domain names have no official status, some are generally regarded as having been unofficially

grandfathered A grandfather clause, also known as grandfather policy, grandfathering, or grandfathered in, is a provision in which an old rule continues to apply to some existing situations while a new rule will apply to all future cases. Those exempt from t ...

, and are unlikely ever to be allocated as top-level domains. Pseudo-top-level domains are also sometimes used for fictitious domain names in video games and other media in order to prevent practical jokers and curious people from either bothering websites and organizations by reaching the domains they see in works of fiction, or registering the domain name in an attempt of

cybersquatting Cybersquatting (also known as domain squatting) is the practice of registering, trafficking in, or using an Internet domain name, with a bad faith intent to profit from the goodwill of a trademark belonging to someone else. The term is derived ...

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