The title given to this article is incorrect due to technical limitations. The correct title isseṭ and aniṭ roots.
The terms set and anit refer to classes of roots in Sanskrit grammar. In the the terminology of Panini, seṭ (from sa-iṭ, Aṣṭādhyāyī 1.2.18, 6.4.121)) means "with (see copulative a) an i-sound), and an-iṭ (Aṣṭādhyāyī 3.1.45, 6.1.188, 6.4.51, 7.2.61) means "without (see privative a) an i-sound". The i sound in question is a phoneme i that appears in certain morphological circumstances for certain, lexically defined roots, regularly continuing PIE Laryngeals.
A root nameserver is a DNS server that answers requests for the root namespace domain, and redirects requests for a particular top-level domain to that TLD's nameservers.
Although any local implementation of DNS can implement its own private root nameservers, the term "root nameserver" is generally used to describe the thirteen well-known root nameservers that implement the root namespace domain for the Internet's official global implementation of the Domain Name System.
There are quite a few alternative namespace systems with their own set of root nameservers that exist in opposition to the mainstream nameservers.