(To be revised, get good links and publish to future HP - coming soon after exams stuff - only if result is okay)
What is Dynamic DNS?

Dynamic DNS is a service (usually free) that let's someone who has a non static IP (Dial-up clients, etc.) who's IP address is changed everytime they connect or in another way, periodically for example, to have a "domain name" that doesn't change as is associated to this changing IP.
Normal Domain services (.com and stuff) take a lot of time to distribute their database, thus changes to your IP, dynamic DNS resides only in one place where you keep your IP address updated in real time (impossible with the .com distributed database that takes weeks to widespread any changes to a domain). There are a lot of free services like this: dyndns.com, yi.org, etc.