As you know, any domain should be pointed to an IP in order to be available in browsers. If you are not connected to the internet with a static IP (cable, DSL, etc.), it becomes tedious to set an A record for your domain every time your IP changes.
Dynamic DNS is a feature that allows pointing a domain name to any IP (static or dynamic). It automatically updates the IP address whenever it gets changed, so that the domain remains connected to the corresponding server.
For example, you have a server at home and host a website on your computer. If you don’t have a static IP, that is, the IP changes each time you reconnect to the Internet, you can set up Dynamic DNS for your domain.