A domain name is the address or name that people type to reach your web site. In some ways, it is like a street address in that it marks your 'corner' of the net or your web real estate. In some ways, domain names are more like phone numbers.
Many people make words or phrases from phone numbers.
This makes it very easy for customers to remember and easy to get in touch when they need a specific product or service. Domains act much the same way. A unique, easy to remember domain helps identify your company or product. Underneath, a domain name is very much like a phone number. It actually IS a number, called an IP address.