Hosting mean to provide a location to place you content . If you had a post-it the soft-board is your host.
Domains are merely names to your site. Remember multiple sites can point to a single host. This is often done by corporates who want to hold on the similar domains. e.g. Yahoo.com and yahoo.co.uk. Domains of the top level are referred to as TLDs. In other words its not a sub-domain. A sub-domain is a section of your site. how ever it will be addressed like products.mysite.com or mail.mysite.com.