DDNS services create permanent names for dynamic IP addresses ( changing ).

DDNS stands for Dynamic DNS, or more specifically, dynamic Domain Name System.
It's a service that maps internet domain names to IP addresses.
It's a DNS service that lets you access your home computer from anywhere in the world.

DDNS serves a similar purpose to the internet's Domain Name System (DNS) in that DDNS lets anyone hosting a web or FTP server advertise a public name to prospective users.

However, 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.
That makes DDNS a good fit for home networks, which normally receive dynamic public IP addresses from their internet service provider.