Answer:
Let's consider an example from Head First CSS and HTMl. Imagine you are the owner of a coffee shop named Starbuzz and because it has grown very popular recently, you want to develop a web site conveying all information related to it. You contact a web-designer, who designs the entire website for you, using a lot of CSS, HTML, PHP and say SQL. Now these files are located inside your computer, which you must transfer to a server computer by FTP (File Transfer Protocol), before they can be accessed by people all over the world. You also require a unique identity, a name, that can be associated only with your website. Say you choose starbuzzcoffee.com. That becomes the domain name of your website. Now you want to expand your website with lots of related web-pages pertaining to, say, business, corporate, employees, etc. So you name those related websites accordingly- business.starbuzzcoffee.com, corporate.starbuzzcoffee.com, employees.starbuzzcoffee.com. Each of these is a website name, that is, they are names around the core- starbuzzcoffee.com, which is the unique domain name, but lots of website names can be created (by you only, of course. The domain name being unique, each website name which contains that as a part of it also becomes yours to name) based on that domain name.