DDNS stands for dynamic DNS, or more specifically dynamic Domain Name System. It's a service that maps internet domain names to IP addresses.
Unlike DNS which only works with static IP addresses, DDNS is designed to also support dynamic (changing) IP addresses, such as those assigned by a DHCP server.

Dynamic DNS Means Anytime, Anywhere Network Access. Because ISPs don't assign static IP addresses, accessing devices your network remotely is tricky.
One way around changing IP addresses is to use PHP-Fusions Dynamic DNS service, which automatically tracks the changes to your network's public IP address and relay this information to our DNS Servers.