Some computers are given a different IP address each time they connect to the Internet. An ISP can use a few IP addresses to serve many customers that way, but it means that your computer's address on the Internet is always changing. If you host a website, you don't want the website name to change
even if your ISP changes the IP address. DNS dynamic update automatically maintains the relationship between your fixed website name and the changing IP address so that your website is easy to find on the Internet.