Domain name: A name by which your website will be known in the internet. These names act as a website’s Universal Resource Locator (URL) in the World Wide Web, which is a home to thousands of websites round the globe.

Internet Protocol (IP) Addresses, which are a series of numbers, are used by the computers to identify each other on the internet. But long numerical digits are tough to remember and so as to why the domain names came into being. They could be easily remembered and used to identify entities in the internet, instead of using an IPA.

A domain name may have one of the following extensions (please note the list below is not exhaustive, only indicative): .com, .net, .org, .tv, .mobi, .biz, .edu

While there is no hard and fast rule to decide on the extension you want for your domain, commercial and business ventures prefer .com (by far the most popular) or .biz.
Non-profit organizations, for example an NGO would use .org
Universities and educational institutes prefer .edu and Government organizations tend to go in for .net domains.

Those building wap compatible sites that can be viewed on mobile phones, tend to use the new .mobi domain name.

At another level, we have country specific domain name extensions, for example .co.uk, .co.jp, .in, .co.in et al. .tv originally a top level country domain for Tuvalu is now being used by TV companies.

Domain Registrar: An Internet Corporation for Assigned Names and Numbers (ICANN) , or Country Code Top-level Domain (ccTLD), accredited company which has the authority to register internet domain names.

Sub-domains: In the Domain Name Systems (DNS) hierarchy, sub domain is a domain that is part of a larger domain. From a point of understanding, Sub-domains are used to organize your website content. A special URL is needed to access them. They are used to create ‘sub-sites’ of the main site. At the very preliminary, non-technical level, sub-domains are folders under the root directory, which are used to structuralize the matters of the main directory. For example, http://www.e2webhosts.com is a regular website or URL without any sub-domain. http://support.e2webhosts.com is an URL with the sub-domain “support”. Syntactically, http://subdomain.domain.com is the basic structure.

To create a subdomain, you login to the cpanel for your hosting account. Click on Subdomains and enter a new subdomain. The cpanel will then create a DNS entry (an A record) for this subdomain to point to your IP address.

Add-On domains: The basic concept related to add-on domain is to run several websites from a single hosting plan or account. An add-on domain creates a sub-directory within the main hosting account but can represent a different website altogether. It shares the web-space and bandwidth with the main domain and collects the information from the sub-domain directory. For example, www.e2webhosts.com is a website’s URL. An add-on domain could be set up such as www.linuxwebhosting.in to point to www.e2webhosts/subdirectory(linuxwebhosting).
So when a visitor visits the site www.linuxwebhosting.in, his browser’s address bar will show http://www.linuxwebhosting.in.
Browsing any pages on this site will show urls referencing http://www.linuxwebhosting.in and there will be no references to the original url – http://www.e2webhosts.com/linuxwebhosting. As you can see it is seamless to the visitor.

Because of this feature of an add-on domain, it is becoming popular with hosting resellers to optimize space on their hosting accounts.

Parked Domains: If you are planning to launch your own website and have also thought of a domain name of your choice, but the website content is not yet ready, then you can purchase the domain name from a domain registrar. By doing so you would be able to place your domain name on a name server so that you can use it whenever you like. This is known as domain parking.

Alternatively, with a parked domain, you don’t have a hosting account associated with it but point it to an existing website. This is accomplished through the URL forwarding feature of the domain. For example, http://www.mysite.com/domain-booking.html deals with domain name transfer, registration, etc and we want to register a separate domain name for this segment which is more memorable, say www.domain-booking.com. Then we can register and park this domain, that is redirect to http://www.mysite.com/domain-booking.html.

The main difference between parked domain and add-on domain is that the URL changes to the original site in parked domains, whereas it does not change in add-on domains. So if a visitor looks at his browser address bar while browsing your site, he will know it is being redirected elsewhere in case of a parked domain.

Domain Aliases: Domain aliases allow multiple domain names all of which lead to the original website. For example, www.e2webhosts.com is a primary domain name for a hosting site with two more names, www.linuxwebhosting.in and say www.e2phphosting.com which are its domain aliases. The visitor to the latter two urls is not redirected towards the original domain name but the matter displayed is the content of the original site.

WhoIs Record: A search engine that provides a detailed record of the domain registrar, the owner of the domain and Domain Name System (DNS) records of an internet entity, for example, a domain, a network, a host, etc. Some of the popular ones to check whois information are:
www.dnsstuff.com
www.whois.sc

Virtual Domain Hosting: Virtual domain in one sentence – is one web server at one IP address, hosting multiple websites with different content and different domain names. A virtual domain utilizes a server’s storage space but is represented by its own domain name.

Devendra Kumar, Simply Ref Check