DNS
"The Domain Name System (DNS) is a hierarchical naming system for computers, services, or any resource participating in the Internet. It associates various information with domain names assigned to such participants. Most importantly, it translates domain names meaningful to humans into the numerical (binary) identifiers associated with networking equipment for the purpose of locating and addressing these devices world-wide. An often used analogy to explain the Domain Name System is that it serves as the "phone book" for the Internet by translating human-friendly computer hostnames into IP addresses. For example, www.example.com translates to 208.77.188.166."
Source: http://en.wikipedia.org/wiki/Domain_Name_System

NS
"In computing, a name server (also called nameserver or DNS server) consists of a program or computer server that implements a name-service protocol. It will normally map (i.e. connect) a human-recognisable identifier of a host (for example, the domain name 'en.wikipedia.org') to its computer-recognisable identifier (such as the Internet Protocol (IP) address 145.97.39.155), and vice versa."
Source: http://en.wikipedia.org/wiki/Nameserver

MX
"An MX record or Mail exchanger record is a type of resource record in the Domain Name System (DNS) specifying how Internet e-mail should be routed using the Simple Mail Transfer Protocol (SMTP). Each MX record contains a preference and a host name, so that the collection of MX records for a given domain name point to the servers that should receive e-mail for that domain, and their priority relative to each other."
Source: http://en.wikipedia.org/wiki/MX_record 

CNAME
"A CNAME record or Canonical Name record is a type of resource record in the Domain Name System (DNS) that specifies that the domain name is an alias of another, canonical domain name. This helps when running multiple services (like an FTP and a webserver; each running on different ports) from a single IP address. Each service can then have its own entry in DNS (like ftp.example.com. and www.example.com.). Network administrators also use CNAMEs when running multiple HTTP servers on the same port, with different names, on the same physical host.."
Source: http://en.wikipedia.org/wiki/CNAME