Round Robin DNS is a simple way of providing load balancing.
One name in DNS is allocated multiple IP addresses. This means that each query to the DNS server returns the next IP address in the list, and then returning back to the start.
This is very rudimentary, and doesn't take into account problems such as one of the servers that is supposed to handle the request going down - in that case, an appropriate proportion of the connections will fail. So it can't be considered a fault-tolerant system.