A __domain name__ is an identification String (computer science) that defines a realm of administrative autonomy, authority or control within the Internet. Domain names are formed by the rules and procedures of the Domain Name System (DNS). Any name registered in the DNS is a domain name - wikipedia 
Strangely there is no clear term for the domain name you register and own, but the term Root domain or more ambiguously __domain name__ can be used.
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- wikimedia
Domain names are organized in subordinate levels (subdomains) of the DNS root domain, which is nameless. The first-level set of domain names are the top-level domains (TLDs), including the generic top-level domains (gTLDs), such as the prominent domains .com, .info, .net, .edu, and .org, and the country code top-level domains (ccTLDs).
# Root domain
The term root domain means different things depending on if you’re talking about the Internet as a whole or about your website.
Technically, the root domain is the highest hierarchical level of the Internet, even above top-level domains such as .com and .net.
What is a root domain?
- raventools.com
Outside of the context of DNS, your root domain commonly means the highest level of hierarchy for the website you control. In the example below, the root domain starts at the microsoft.com node and includes everything branching from it in blue.
# Use
Below these top-level domains in the DNS hierarchy are the second-level and third-level domain names that are typically open for reservation by end-users who wish to connect local area networks to the Internet, create other publicly accessible Internet resources or run web sites.
Domain names are used in various networking contexts and for application-specific naming and addressing purposes. In general, a domain name represents an Internet Protocol (IP) resource, such as a personal computer used to access the Internet, a server computer hosting a web site, or the web site itself or any other service communicated via the Internet. In 2017, 330.6 million domain names had been registered.
The registration of these domain names is usually administered by domain name registrars who sell their services to the public.
# Fully qualified domain name
A fully qualified domain name (FQDN) is a domain name that is completely specified with all labels in the hierarchy of the DNS, having no parts omitted. Labels in the Domain Name System are case-insensitive, and may therefore be written in any desired capitalization method, but most commonly domain names are written in lowercase in technical contexts.
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# See also