Its showing the response time and quality of DNS servers. If you are having slow internet response and load times this tool could help you by finding a quicker DNS server. It details the DNS server IP Address as well as the, Min, Average,and Max, response time (lowers is better) and the server reliability. Here is a link to give you more detail of what a DNS server does.
http://dyn.com/blog/dns-why-its-important-how-it-works/