What is a root, in the Internet?
It is a directory containing domain names of TLD level, as: de, fr, uk, com, org. Every name is unique in a root. Each name is associated with one or more IP addresses.
The function of such a directory is to provide a user (usually a browser) with an IP address of a sub-directory containing the next part of the domain name.
E.g. finances.gouv.fr.
a- the root provides the IP address of the fr directory,
b- the fr directory provides the IP address of the gouv directory,
c- the gouv directory provides the IP address of the finances directory,
d- the finance directory provides the IP address of the target site.
The root is the first step in searching for the target site. Its contents is limited to TLDs and associated IP addresses.