when asked what your domain name is, know that that really means what your hostname is.

What is a Second Level Domain?


Second level domain, also known as a sub-domain, is similar to a domain, so getting confused is very easy. Basically, a sub-domain is not similar to domain in that it is part of a large domain. For example, elftest.net is a domain since it’s the solid basis on which all websites are built. On the other hand, tools.elftest.net is a sub-domain in that it is the domain’s subset. Take note of how ‘tools’ is placed before elftest.net. That additional period between the two words, i.e. tools and elftest, is the only way we know tools.elftest.net is a sub-domain. The .net part is what is called TLD, or Top Level Domain, and when you see ‘www,’ you know that it is not a sub-domain, but just a special term.

For now, let’s ignore protocol and look at the following:

  • URL: http://www.example.com/index.html
  • TLD: com
  • Second level domain name: sub.example.com
  • Hostname: example.com or example.com

You wonder why ‘www’ is so special. During internet inception, this is how people used to identify a web page, although these days the ‘www’ is sometimes dropped since we use ‘http’ these days. Although we feel that ‘www’ unnecessary makes URLs longer, note that http://elftest.net and http://www.elftest.net will always take you to the same place. This means that ‘www’ can be considered a second level domain, but it is special in that it points you to the same place as when you exclude it from the domain. In most cases, when asked what your domain name is, know that that really means what your hostname is.

The second level domain

Second level domain, also known as a sub-domain, is similar to a domain, so getting confused is very easy.

From the examples above, it is clear that a domain is example.com and a second level domain is sub.example.com. If you are on WordPressMultisite and you are asked what a mapped domain is, and what the second level domain points to, you should answer mappeddomain.com points to mapped.example.com.

Please do not ever use domain mapping plugins as your second level domain as they are mature domains only. Note that TLDs are what you see in things such as example.co.uk. It is not a second level domain since the main domain is .co.uk which makes part of the primary URL, not the subset. You will find tech-savvy people who want to confuse you, but this information will help you identify some of their confusing features with a clear focus.

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