Round-Robin DNS is a simple mechanism for managing DNS load balancing. This task is not done through hardware but via a DNS server known as an authoritative nameserver.
When you deploy Round-Robin in a DNS server, this will save different A records. Each of them has different IP addresses, but all with the same domain name. Every time this DNS record is requested, it will deliver a response (IP address) by its order. And every IP address used to respond to a request will be put at the end of a line to be used again. You have multiple IP addresses working on a constant rotation cycle.
This mechanism is really useful if you have your website’s content hosted on different redundant servers located at separate points of the globe. The authoritative nameserver will use this rotation cycle to answer with a different IP address. By doing so, it will load balance the traffic.