Thankfully, you don’t need to memorise all of the below as it can get a little confusing. As a registrant; usually all you need to be able to distinguish between is a domain name – the popular terms used collectively for second and third level domains – and a subdomain.
TLD – Top Level Domains
These are at the highest level in the DNS structure of the Internet. There are several different types of TLD’s, being:
ccTLD – country code Top Level Domains
Two letter domains established for geographical locations; for example; .au signifies Australia. When originally designated, usually only residents of a country could register their corresponding ccTLD; but over the years quite a few countries have allowed parties outside their shores to register website names. An example of this is Tuvalu (.tv).
In the case of .au domain names, strict rules are still in place (and that’s a good thing). For example, .com.au registrants must still be Australians or have registered business interests in Australia. The registration eligibility criteria for au names has meant .au is still strongly associated with Australia and has fostered a great deal of trust and confidence among local and even overseas online shoppers.
gTLD – generic Top Level Domain
The best known generic TLD’s include .com, .net, .biz, .org and .info – these can be registered by anyone, anywhere in the world. However, some of the new gTLD’s more recently released have various restrictions.
IDN ccTLD – internationalised country code top-level domains
A top-level name with a specially encoded format that allows it to be displayed in a non-Latin character set (i.e. special characters).
Below the TLD’s are various other levels:
Directly below a TLD in the DNS hierarchy, e.g. .com.au
Directly below a second level in the DNS hierarchy. e.g. domainregistration.com.au
The difference between second and third level can be a little confusing. For example, hotmail.com is considered a second level domain, but hotmail.com.au would be classed as a third level.
Part of a higher ranked domain name in DNS hierarchy; e.g. example.domainregistration.com.au.
Some services offer subdomain “registration” – but this usually isn’t ideal for businesses and should probably be avoided for establishing a commercial website as the registrant of the upper hierarchy name has control over the address. Having your own name can also help with credibility.