DNS (Domain Name System) is the system that translates an Internet name (that is easier for people to remember) to an IP address. A Domain Name could be for example https://www.networkstraining.com that the DNS translates to an IP address (74.54.219.242). If the address is registered in a reverse lookup zone, the IP address is translated back to the DNS name and it is called “reverse DNS lookup” or simply r-DNS.
A DNS system consists of two parts: a server and a resolver. The server keeps information about which DNS names correspond to which IP addresses. A Resolver is the software on the DNS client who is asking the server for information.
A DNS name consists of a host (e.g www means it is a webserver) and domain (e.g networkstraining.com). Domains are unique and are recorded in global databases.