Dynamic IP Update Service is simply a way of attaching a static hostname to a dynamic IP address.
On the Internet, there are a limited number of IP addresses. When you connect to your ISP, you are assigned a temporary IP address that other computers use to find you while you are connected. Once you disconnect, that IP address is given to someone else, and so on. If you are trying to operate a gaming server, personal web server, or any other service that requires other computers to be able to find you, they need to know what your IP address is. This is not easy if your IP address is dynamic, like most people`s are, because you will have to keep telling everyone what your current IP address is (comparable to changing your phone number every day). With a dynamic DNS service, like DtDNS.com, DynDNS.org, NO-IP.com and 2myDNS.com, you can get a static name to attach to that ever-changing IP address. Now, you just give out your static hostname instead of your IP address, and only tell the service what your IP address is. This way everyone will be able to find you quickly when you are online.
Dynamic IP Update Service automatically updates your IP at the dynamic DNS service everytime it changes. It is implemented as a reliable, managed Windows Service.