A Dynamic IP address is one that is not static. It changes from time to time. If you are unsure if your IP address is static or dynamic, chances are pretty high that it is dynamic. They are more cost effective for your ISP (Internet Service Provider).
Imagine that once a day at a random time your phone company changed your telephone number. If there was no way to look it up no one would be able to call you! This is what a dynamic IP address effectively is. It’s a changing phone number. The number used to find your computer on the Internet can be different each time you log on, or at the discretion of your ISP. Dynamic DNS is like a live phone book that updates itself when your number changes. It knows your number at any given time so that people can connect to you. To make sure the dynamic DNS server has your proper IP address, your computer must run an update client to let the server know when your IP address has changed.