Dynamic DNS allows you to dynamically update your DNS records if you have a Dynamic IP address from your ISP. You install an app on a computer on your network, and it checks your WAN IP address periodically and then updates your DNS records.
NoIP.com and DynDNS.org are the most prominent Dynamic DNS Providers. You can either buy your domain name from them, or you can forward your domain name to a subdomain you create with them. i.e. FailedNormal.com — FailedNormal.no-ip.com