A website domain name is a unique address that can be used on the interent.  It is what you see in the address bar after the "www." in your web browser and it is what comes after the @-sign in an email address. 

Domain names consist of two parts.  For example in the "wsicyprus.com", the ".com" represents what is known as the top level domain (TLD) and "wsicyprus" represents the second level domain and is the actual name.  The same domain can be used with different TLDs such as .biz, .org, .net.  There are also country-specific Top Level Domains, such as .com.cy (for Cyprus), .gr (for Greece), and .fr (for France). 

When a domain is used in a web address, 'www' is usually put in front of if to indicate that typing that name in your web browser will take you to a website.  Domain name holders can set up a website with that address and also use it for email addresses.  When you use a domain name holder you get to decide what is in front of the @-sign in the email address.

Registering a domain name doesn't automatically make your website appear when visitors enter your domain into a Web browser. You have to upload your website to a computer that hosts the site and assigns a numeric address, called an IP address, to your domain. Your domain and associated IP address are stored in a database with every other domain and associated IP address. When visitors enter your domain into a Web browser, your domain works like an address forwarding service by forwarding visitors to the IP address where your website is stored. We use domain names instead of IP addresses because most people find it easier to remember a name rather than a series of numbers.

When you register a domain, you do not have to create and upload a website. You can also:

The more domains you register, the better. Prevent others from registering a similar domain to yours—just to steal away your customers. What to do with all these names? Forward them to your main domain.