.arpaThe domain name arpa is a top-level domain (TLD) in the Domain Name System (DNS) of the Internet. It is used predominantly for the management of technical network infrastructure. Prominent among such functions are the subdomains in-addr.arpa and ip6.arpa, which provide namespaces for reverse DNS lookup of IPv4 and IPv6 addresses, respectively. The name originally was the acronym for the Advanced Research Projects Agency (ARPA), the funding organization in the United States that developed the ARPANET, the precursor of the Internet.
Generic top-level domainGeneric top-level domains (gTLDs) are one of the categories of top-level domains (TLDs) maintained by the Internet Assigned Numbers Authority (IANA) for use in the Domain Name System of the Internet. A top-level domain is the last level of every fully qualified domain name. They are called generic for historical reasons; initially, they were contrasted with country-specific TLDs in RFC 920. The core group of generic top-level domains consists of the com, net, org, biz, and info domains.
.eduThe domain name .edu is a sponsored top-level domain (sTLD) in the Domain Name System of the Internet. The domain was implemented in 1985 to create a domain name hierarchy for organizations with a focus on education. At the time, it was open for registration for entities from any region. Since 2001, new registrants for second-level domain names have been required to be United States–affiliated institutions of higher education. List of the oldest currently registered .
.govThe domain name gov is a sponsored top-level domain (sTLD) in the Domain Name System of the Internet. The name is derived from the word government, indicating its restricted use by government entities. The TLD is administered by the Cybersecurity and Infrastructure Security Agency (CISA), a component of the United States Department of Homeland Security. gov is one of the original six top-level domains, defined in RFC 920. Though "originally intended for any kind of government office or agency", only U.S.
Country code top-level domainA country code top-level domain (ccTLD) is an Internet top-level domain generally used or reserved for a country, sovereign state, or dependent territory identified with a country code. All ASCII ccTLD identifiers are two letters long, and all two-letter top-level domains are ccTLDs. In 2018, the Internet Assigned Numbers Authority (IANA) began implementing internationalized country code top-level domains, consisting of language-native characters when displayed in an end-user application.
VerisignVerisign Inc. is an American company based in Reston, Virginia, United States, that operates a diverse array of network infrastructure, including two of the Internet's thirteen root nameservers, the authoritative registry for the , , and generic top-level domains and the country-code top-level domains, and the back-end systems for the and sponsored top-level domains. In 2010, Verisign sold its authentication business unit – which included Secure Sockets Layer (SSL) certificate, public key infrastructure (PKI), Verisign Trust Seal, and Verisign Identity Protection (VIP) services – to Symantec for $1.
.us.us is the Internet country code top-level domain (ccTLD) for the United States. It was established in early 1985. Registrants of .us domains must be U.S. citizens, residents, or organizations – or foreign entities with a presence in the United States or any territory of the United States. Most registrants in the U.S. have registered for .com, .net, .org and other gTLDs, instead of .us, which has primarily been used by state and local governments, even though private entities may also register .us domains.
Top-level domainA top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain. The top-level domain names are installed in the root zone of the name space. For all domains in lower levels, it is the last part of the domain name, that is, the last non empty label of a fully qualified domain name. For example, in the domain name www.example.com, the top-level domain is .com. 