If you have a device on your network, such as a security camera or even a server that you want to access remotely, this can be difficult without a static IP address. An IP address is a number assigned to each device on a network that uses the internet. For most home users with residential internet service, this number can change periodically. When that number changes, it is referred to as a Dynamic IP address. It's possible, however, to pay more to get a Static IP address, which doesn't change. When the address is static, it's much easier to access devices and servers remotely.
There are ways around this, though, so that you can still access devices from your network despite having a Dynamic IP. One option is DynDNS. With DynDNS, you'll choose a unique hostname and link it to an IP device. As the IP addresses used to access these devices change, Dyn will make sure to update it for you. This service costs around $40 a year.