Dns

https://www.cloudflare.com/learning/dns/what-is-dns/

https://aws.amazon.com/route53/what-is-dns/

DynDns

Dynamic DNS is used when no static IP address is available. This is often the case with domestic connections. DynDns allows the record to be automatically updated, when the address changes. This is done by having a program call out to the DNS servers, whenever a change occurs.

https://en.wikipedia.org/wiki/Dynamic_DNS

Methods of doing so are often supplied by the domain name registrar.