A domain name is the root web address for a Website, such as about.com .
A website's domain may include one or more subdomains. A subdomain is a specific section within the domain, such as homebusiness.about.com.
Only one person or entity may register a given domain name. It is not necessary to register a subdomain. Once registration expires, someone else can register and use it as their domain name. A business or individual can register as many domain names as desired.
Some people have made a business out of registering domain names that they speculated would be in high demand and then selling them to the highest bidder.
Domain names are often used in branding. The about.com domain is a good example, as is amazon.com or travelocity.com. The names of these business are instantly recognizable.
Domain names are also selected for search engine optimization (SEO) purposes. For example, if one wanted to secure a domain name that would rank well for the search term "cars", they might register the name cars.com. In the past, search engines would give added weight to domain names that included the keyword that was being searched for. As search engines have matured, the domain name is becoming less of a factor in search rankings, although it can still make a difference.
