Domain name is a name that identifies a computer or computers on the internet. These names appear as a component of a Web site's URL, e.g. kolkatawebhosting.org. This type of domain name is also called a hostname. Domian name is also known as the product that domain name registrars provide to their customers. These names are often called registered domain names.
The most common types of domain names are hostnames that provide more memorable names to stand in for numeric IP addresses. They allow for any service to move to a different location in the topology of the Internet (or an intranet), which would then have a different IP address.
By allowing the use of unique alphabetical addresses instead of numeric ones, domain names allow Internet users to more easily find and communicate with web sites and other server-based services. The flexibility of the domain name system allows multiple IP addresses to be assigned to a single domain name, or multiple domain names to be assigned to a single IP address.
Hostnames are restricted to the ASCII letters "a" through "z" (case-insensitive), the digits "0" through "9", and the hyphen, with some other restrictions. Registrars restrict the domains to valid hostnames, since, otherwise, they would be useless. The underscore character is frequently used to ensure that a domain name is not recognized as a hostname.
ICANN (Internet Corporation for Assigned Names and Numbers) has overall responsibility for managing the DNS. It controls the root domain, delegating control over each top-level domain to a domain name registry. For ccTLDs, the domain registry is typically controlled by the government of that country. ICANN has a consultation role in these domain registries but is in no position to regulate the terms and conditions of how a domain name is allocated or who allocates it in each of these country level domain registries. On the other hand, generic top-level domains (gTLDs) are governed directly under ICANN which means all terms and conditions are defined by ICANN with the cooperation of the gTLD registries.
Domain names which are theoretically leased can be considered in the same way as real estate, due to a significant impact on online brand building, advertising, search engine optimization, etc.
A few companies have offered low-cost, below-cost or even free domain registrations, with a variety of models adopted to recoup the costs to the provider. These usually require that domains are hosted on their site in a framework or portal, with advertising wrapped around the user's content, revenue from which allows the provider to recoup the costs. When the DNS was new, domain registrations were free. A domain owner can generally give away or sell infinite subdomains of their domain, e.g. the owner of example.edu could provide domains that are subdomains, such as foo.example.edu and foo.bar.example.edu.
Please make sure that the domain name is registered under your name and that registrant and billing contact email address has been set as your email address, as some competent website hosting providers register the domain names under themselves, and they might refuse to transfer the domain names once you want to switch to some other providers. You can check your domain information through any public whois registry, for example http://www.whois.net.