In summary, DDNS stands for Dynamic DNS. DDNS updates a DNS name in real-time to point to a changing IP address. This is useful for devices without a static IP. For example, companies like Google use static IPs and IP ranges, which are more expensive than ephemeral IPs and IP ranges. DDNS provides a cost-effective alternative, linking a hostname to a dynamic IP address.
To use DDNS, you need an account with a DDNS provider. While some services are paid, they are still cheaper than static public IPs from ISPs. A script or service on your device updates the DDNS server with your current IP at regular intervals to maintain the link between your hostname and IP address. Luckily for us, DuckDNS is free for everybody and relays on donations to keep their services running.