The domain name is the address of your website, the part that can take you to the front door, so to speak. For example, our domain name is pushon.co.uk!
Your domain name needs to be recognisable and, of course, related to your brand. This is why you rarely see sites use something different to their brand name when creating a website.
The domain name also contains the TLD, which helps to identify what geographic area your site pertains to or even what type of organisation it is.