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When you search term Apex Domains on Google Search, the top page you get is https://help.github.com/en/articles/about-supported-custom-domains, which explains the concept as:

An apex domain is a root domain that does not contain a subdomain part. Apex domains are also known as base, bare, naked, root apex, or zone apex domains. In DNS provider settings apex domains are sometimes symbolized by an @ symbol. For example:

  • example.com is an apex domain because it doesn't have any subdomain parts.
  • Whereas www.example.com is not an apex domain because it contains the > subdomain part www.

This description alone says this concept is also known as

  • base domains
  • bare domains
  • naked domains
  • root apex domains
  • zone apex domains

Is there really not a well-recognized and established name for this concept?

ahmet alp balkan
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    Eh, it's a **root domain.** You can put all kinds of lipstick on a root domain (including a subdomain) and the root domain remains intact. – Robert Harvey Apr 01 '19 at 18:22
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    BTW feel free to add as an answer with maybe a bit more elaborating your argument, happy to accept after a few answers. – ahmet alp balkan Apr 01 '19 at 18:39

1 Answers1

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If you want to be 100% technically correct, this latest RFC from the IETF does give precise information on all DNS terminology.

https://www.rfc-editor.org/rfc/rfc7719 "DNS Terminology".

Note that this deals with technical terms, not marketing ones.

If you search for apex in it you get:

Apex: The point in the tree at an owner of an SOA and corresponding authoritative NS RRset. This is also called the "zone apex". [RFC4033] defines it as "the name at the child's side of a zone cut". The "apex" can usefully be thought of as a data-theoretic description of a tree structure, and "origin" is the name of the same concept when it is implemented in zone files. The distinction is not always maintained in use, however, and one can find uses that conflict subtly with this definition. [RFC1034] uses the term "top node of the zone" as a synonym of "apex", but that term is not widely used. These days, the first sense of "origin" (above) and "apex" are often used interchangeably.

In light of this, github definition is slightly wrong. example.com is the apex of the zone example.com (because it is delegated from .com, that we know for sure), that has www.example.com in it.

Speaking about domains and subdomains is something opening to many perils, as you can not judge, just by looking at the string, where the zone cuts are, hence where the "subdomain" starts. Examples to study: www.dk, www.minefi.gouv.fr to start with.

Just by looking at www.example.com (without doing any kind of DNS queries) you can not say if www is just a label inside the example.com zone, or if www.example.com is an apex because it has been delegated from example.com. Of course, one might argue that www gives an hint, but then replace it with admin, and the mystery remains unsolved.

Community
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Patrick Mevzek
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    At the time this answer was written, RFC 7719 was already obsolete! But to be fair, only by a few months. It is updated by [RFC 8499](https://www.rfc-editor.org/rfc/rfc8499), which fortunately contains the same definition as given above. – Medlock Perlman Nov 04 '21 at 10:35