DNS is the Domain Name System is one of the most important services in many IP-based networks. Its main task is to answer inquiries about name resolution. The DNS works much like a telephone directory inquiry.Dynamic DNS, DDNS or DynDNS is a technique for dynamically updating domains in the Domain Name System. The purpose is that a computer automatically and quickly changes the associated domain entry after changing its IP address.
DNS is what allows devices and browsers to translate a human readable address into an IP address which for a lot of people is more difficult to remember. Without DNS, typing in google.com is going to get you no where.
Dynamic DNS is a method that lets you automatically attempt to update name servers and remain up-to-date with IP address changes in or nearly in real-time.
DNS is in most cases an absolute must, whereas DDNS is not required but will be nice to have if your project has the need.