Domain names - Domain names are the word sequences users enter in their address bar of an internet navigator to visit a specific web site. Each domain name is assigned to an IP address. The DNS ( Domain Name System ) is used to translate the IP addresses into words.

For example: wallpaperama.com is this website's domain name

How about www.wallpaperama.com? - the www is called the host name, or sub domain name that belongs to the domain name wallpaperama.com. it could be anything you want, like example.wallpaperama.com. the www stands for world wide web.

What are co-domain names? Co-domain names are the same as sub domain names.