What is the different between domain and subdomain?

A domain name is a full website address totally independent of other domain names, but a subdomain depends on a domain name. If for example "yourdomain.com" is your domain name, then http://yourdomain.com and http://www.yourdomain.com would be your domain name's address.

A subdomain name would be a name under your domain name, something like "sales.yourdomain.com". It's address would then be: http://sales.yourdomain.com. It can say anything you want instead of "sales" and the nice thing is that unlike a domain name, a subdomain does not need to be registered. This will save you money.