A dynamic IP address is an IP address that is not static, meaning it can change from time to time. Most cable and DSL services use dynamic IP addresses because they are more cost effective. Even though your IP address is classified as dynamic, it is possible that it may stay the same for days, weeks or even months at a time. This all depends on your Internet Service Provider.
Check out the services No-IP offers to help keep your dynamic IP address updated and your server running.