Domain names are the unique, human-readable Internet addresses of websites. They are made up of three parts: a top-level domain (sometimes called an extension or domain suffix), a domain name (or IP address), and an optional subdomain.
The combination of only the domain name and top-level domain is known as a “root domain.” The “http://” is part of a page’s URL but not its domain name and is known as the “protocol.”
Let’s look at each of these elements more closely:
Top-level domain (TLD) is the formal term for the suffix that appears at the end of a domain name. Some example of top-level domains include:
While we’re probably all familiar with the TLDs above, there are actually over 1,000 possible TLDs from which webmasters can choose. This includes things like .book, .clothing, .dog, and .lifeinsurance (to name a few), as well as TLDs associated with specific countries or territories like .uk (United Kingdom) or .dk (Denmark). These country- (and sometimes region-)specific TLDs are known as country code top-level domains, or ccTLDs.
Domain names are the second level of a domain’s hierarchy (after the top-level domain). Domain names on a specific TLD (called a root domain, discussed below) are purchased from registrars and represent the specific, unique location of a website. In the following examples, the domain names are bolded:
- www.example.o… engines do use the keywords in domain names as a ranking factor (which explains the existence of domains like “where-to-buy-the-best-donuts-in-Seattle.com”), but tread lightly when thinking about optimizing your root domain for search engines: One of the specific functions of Google’s algorithm is to combat these keyword-stuffed exact-match domains.
While the term “root domain” was originally created in the context of DNS (domain-name servers), it typically refers to the combination of a unique domain name and a top-level domain (extensions) to form a complete “website address.” Your website’s root domain is the highest page in your site hierarchy (probably your homepage). Individual pages or subdomains can be built off the root domain, but each page URL must technically include the same root domain in order to be a part of your website.
Examples of root domains include:
All the pages on a single website have the same root domain (discussed below), and no two different websites can have the same root domain.
Because root domains represent whole websites instead of specific web pages, counting linking root domains instead of linking URLs (pages) can be a more accurate way to judge the size of your site’s inbound link profile (generally speaking, more linking root domains is better). Backlink tools like Link Explorer or Majestic can help uncover the total number and specific identity of root domains linking to your site.
Subdomains are the third level of a domain’s hierarchy and are parts of a larger top-level domain. They are added in front of the root domain and separated from the domain name with a period.
For example, “blog.example.com” and “english.example.com” are both subdomains of the “example.com” root domain. Subdomains are free to create under any root domain that a webmaster controls.
The two most common subdomain choices are:
- http://www.example.com (“www” is the subdomain)
- http://example.com (has no subdomain)