Root servers are the authoritative name servers that serve the DNS root zone. There is a network of hundreds of root servers around the world. The root servers contain the information that makes up the root zone, which is the global list of top level domains.
The root zone contains:
generic top level domains – such as .com, .net, and .org
country code top level domains – two-letter codes for each country, such as .ME for Montenegro or .NO for Norway
internationalized top level domains – generally equivalents of country code top level domain names written in the countries’ local character sets.
For each of those top level domains, the root zone contains the numeric addresses of name servers which serve the top level domain’s contents, and the root servers respond with these addresses when asked about a top level domain.