What is DynDNS/DDNS
DynDNS or DDNS is a technique to dynamically update domains in the Domain Name System. The purpose is that after a computer changes its IP address, it automatically and quickly changes the associated domain entry.
This means that the computer can always be reached under the same domain name, even if the current IP address is unknown to the user. We support both IPv4 and IPv6.
Use of DynDNS services
A typical use case for dynamic DNS over HTTP or HTTPS is a home user's computer that has access to the Internet via a dynamic IP address from the Internet service provider. For example, if the user wants to operate a game server or access the computer from outside via a remote desktop, they would have to know the constantly changing IP address. With dynamic DNS, he can instead register a domain name with a DDNS provider and automatically assign the current IP address to the name.
Quelle: German Wikipedia Article