Round Robins Dns is a simple form of load ballancing, you have 2 or more servers which provides the same servive e.g. irc or www. You want half of the users to use server A and the other half to use server B.
But users are stupid they cant figure out which server to connect to so therefore you can create a round robin dns entry.
In its simple mind its all about two A-record in you dns, if you make:
myservice.org IN A 192.168.0.1
myservice.org IB A 192.168.0.2
The first request for myservice.org will get 192.168.0.1 the next 192.168.0.2 and so on. I know of no limit on this.