What is a Hostname?
As it is rather complicated to memorize IP addresses, most people use Domain Names instead. Domain name looks like www.company.com.The resolution between domain names and IP addresses is handled by the Domain Name Servers (DNS).
Since IP numbers are usually assigned to internet service providers within country-based blocks, an IP address can often be used to identify the country, where the computer is connecting to the Internet.
Please note that it is IP address (not domain name), that defines host location.
What is a dynamic DNS? Heavy load web sites may use multiple IP addresses for a single domain name, as forwarding traffic to different computers allows implementing load balancing. Try submitting this form for yahoo.com once each 5 seconds for example. You should notice that the yahoo.com resolves to different IP addresses in random order.