The article explains a Domain, and what is a DNS or Domain Name System before talking about how DNS Lookup works and does.

The Domain Name System (DNS), one of the foundations of the internet, resolves the names of internet sites with their underlying IP addresses, adding efficiency and security in the process.

Domain Name System (DNS) servers translate human readable host or domain names to numeric IP addresses. Drexel IT Networking manages domain name servers used by the university. At start-up time, most ...

When your DNS server receives a request for a domain it has no authority over, it forwards it to another DNS server (or performs the lookup itself using the root servers).

Most organizations have at least two authoritative domain name servers, but some handle so many DNS requests that they need to spread the load over additional DNS server domains.