The very first set of domain names are known as the top level domains (TLDs), the generic top level domains (gTLDs) (e.g org, com and net domains) and the country code top level domains (ccTLDs).
Domain names are pertinent in myriad networking contexts, application specific naming and for more obvious purposes of addressing – apart from first level domains there are second level and third level domain names and they are critical to end users for among other things the creation of publicly accessible internet resources.
the domain name system host names are leaf labels and they appear as a component in Uniform Resource Locators (URLs), a domain name serves as a means to indicate ownership and identification labels, thus short and memorable names are more desirable.
Characteristically domain names can contain only ASCII letters, numbers and the hyphen (-) and the full stop (dot, .) separates DNS labels, and to cater for other non-English languages whose characters are rendered incompatible such as Asian languages. Which may require multi byte characters, a group of top level domains under testing to deal with the issue under the internationalized domain name (IDN) system.
Another variation is that the underscore character is utilized to make certain that a domain is distinguished from a host name, and such domain names are in some instances used were hostnames are needed.
Registration of domain names through a registrar does not necessarily translate to legal ownership but only exclusive rights of use, and due to heavy numerical differences between websites and servers the hypertext transfer protocol (HTTP) stipulates that the client informs on the name under utilization. And to ensure a single server with one IP address lists various sites for different domain names, known as virtual hosting.
In the early days the country code top level domains (ccTLD) used the two character territory codes of ISO-3166 country abbreviations, and seven generic top-level domains (gTLD) representing a number of categories of names and multi organization were initiated (gov, edu, com, mil, org, int and net.
Thirteen more gTLDs were implemented by June 2009 and ccTLD’s stand at 248 domains, while second level domains (SLD) consist of names that are essentially to the left of com, and net among other top level domains (e.g en.example.net, example belongs to the second level domain).
And third level domains are immediately to the left of a second level domain and fourth and fifth level domains are also possible, an example of fourth level domain name is fbo.state.oh.net.