With a static IP address, the IP address does not change. With a dynamic IP address, the IP address can change.
Reasons to want a static IP address include needing to remotely access your home or work network, remote camera viewing, and running game or media servers. With a dynamic IP using such services can be difficult because you would have to find methods to get the new IP address each time it changes.
Windstream offers both static and dynamic IPs. Customers normally start with dynamic IP addresses but static IP addresses are available for an additional cost.