Dynamic DNS is a system that allows the domain name data held in a name server to be updated in real time. The most common use for this is in allowing an Internet domain name to be assigned to a computer with a varying (dynamic) IP address. This makes it possible for other sites on the Internet to establish connections to the machine without needing to track the IP address themselves. A common use is for running server software on a computer that has a dynamic IP address, as is the case with many consumer Internet service providers.
Dynamic DNS service is provided on a large scale by various DNS hosting services, which retain the current addresses in a database and provide a "client" program to the user that will send an update to the service whenever the server's IP address has changed. Many commercial and freely available providers exist that provide Dynamic DNS services including everydns.net and no-ip.com amongst many others.
The benefits of using Dynamic DNS for users that do not have statically assigned IP addresses are quite important in that they are able to host their own websites, IRC / chat servers and other such services, even mail servers. Unfortunately hosting DNS with a dynamic IP address is not possible and having Dynamic DNS services to your IP address still cannot help with that as DNS servers are accessible via their IP address and not via an FQDN.
Users with static IP addresses are always better off not using Dynamic DNS, instead they should configure direct DNS services to point to their address. Dynamic DNS requires a large amount of polling and a low threshold of DNS cache expiry in order to recover from changes to the underlying IP address.On the other hand, for statically assigned IP addresses there is no reason to incur such overheads since we know that the address will remain the same over time.