DNS is Domain Name System (or Service)

you have the domain cheatatyourgames.tk and it is a DNS server that tells our computers which IP address www.cheatatyourgames.tk points at. DNS also holds the email routing information for each domain and can hold a great deal more as well

Each domain has a number of name servers defined for it, when someone trying to get DNS data for a domain, a look up of the central registry for that domain type will return the specific Name Servers that will have the necessary information, these will then be used to get the necessary information

For a full descrition you could have a read over some of the RFCs conerning DNS
http://www.dns.net/dnsrd/rfc/
Though this might be heavy going.