DNS is one of the fundamental building blocks of the internet. It is what translates a domain name (amazon.com) into the physical internet protocol address where amazon.com can be found. Without it, we would not be able to navigate using domain names.
From root-servers:
Events of 2015-11-30
On November 30, 2015 and December 1, 2015, over two separate intervals, several of the Internet Domain Name System's root name servers received a high rate of queries. This report explains the nature and impact of the incident.
While it's common for the root name servers to see anomalous traffic, including high query loads for varying periods of time, this event was large, noticeable via external monitoring systems, and fairly unique in nature, so this report is offered in the interests of transparency.
Probing - always probing. More at the link (prettty geeky stuff).