All devices that connect to the internet are assigned a numeric address. These are called IP addresses. These numbered addresses would be a nightmare for humans to use if it wasn't for DNS, the Domain Name System.
Imagine for a moment. Opening your web browser, but instead of entering "Google.com", you have to type 126.96.36.199. Remembering the addresses of all the sites you use would quickly become troublesome. Error-prone and frustrating.
Enter DNS, which translates human-readable names to IP addresses. DNS works in a similar way to a Phone Book. For younger readers, a phone book was a large book published by your local phone provider, which listed everyone's name and phone number. Rumor has it, they still exist. But I haven't seen one in many years. In the same way, a phone book tells you your uncle Tom's phone number, DNS translates a domain name to an IP address.
There are two types of DNS services. Authoritative and Recursive.
Authoritative DNS is where a Domain Name lives. A domain normally has two or three Authoritative DNS servers listed on their domain registration. These servers are where all the records live and are the only place they can be changed.
Recursive DNS is another story. When you enter a domain name into your browser, your computer isn't reaching out to the Authoritative server for the domain. It instead queries the Recursive DNS service provided by your ISP (Internet Service Provider.) Your local Recursive DNS service then checks its cache to see if it already knows the address. If it doesn't know, or its cached records are too old, it then reaches out to the authoritative DNS. In this fashion, DNS becomes somewhat distributed, takes a load off the authoritative servers and speeds up your browse time.
This has been an introduction to the Domain Name System, but getting you to your favorite website is only the beginning. DNS also directs the flow of e-mail. It's used for domain ownership verification of web services. Even SPAM protection using SPF(Sender Policy Framework) and DKIM(DomainKeys Identified Mail) records.
For more detailed information see https://en.wikipedia.org/wiki/Domain_Name_System
The RFC section in particular.
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