A SLD or “Second Level Domain” is all often called the “domain” or “base domain.”
Most of the time when people buy a domain, they are buying a Second Level Domain. To get even more specific, they are buying a SLD + TLD combination.
When a ccSLD – or “country code Second Level Domain” – is used, then a user will actually be buying a third level domain.
ccSLDs can make it difficult for developers to deal with domains, in the sense that many developers have to parse out URLs for many reasons, but there is no hard set rule on how to parse a domain out. You just have to have a comprehensive list of all ccSLDs and their corresponding ccTLDs in order to properly distinguish the users “base domain” from their “domain extension.”
A “domain extension” is slang for “Top Level Domain” or “country code Second Level Domain + country code Top Level Domain”.
In other words, if you buy “example.com” – “example” is your “base domain” and “.com” is your domain extension. In this case, your base domain is your “Second Level Domain” and your domain extension – “.com” is your TLD.
On the other hand, if you buy “example.co.uk” then “example” is still your base domain but “.co.uk” is your “domain extension”. In this case, your “base domain” is your “Third Level Domain”, and your “domain extension” – “.co.uk” – is your SLD + TLD.
A “TLD” or “Top Level Domain” is also commonly known as a “domain extension.”
We actually just prefer the term “domain extension.”
Examples of TLDs are:
Examples of ccTLDs are:
A ccSLD – or country code Second Level Domain, is often mistaken for a TLD, however they are actually two separate domain levels. For example “.co.uk” is two domains: “.co” os a ccSLD and “.uk” is a ccTLD.
See SLDs and ccSLDs.
How do I use PHP’s parse_url() function to separate out the base domain from the domain extension?
How do I use PHPto extract the domain from a URL?
How do I extract the domain when it is using a ccSLD, or “country code second level domain”, such as .com.au and .co.uk?
PHP’s parse url function is quite handy, but not all powerful, and it cannot distinguish between domains and subdomains. (more…)