The Domain Name System (DNS) is a critical part of Internet infrastructure. It's managed by ICANN (the Internet Corporation for Assigned Names and Numbers).
Similar to an index of a book, the DNS provides a systematic and hierarchical way of storing and accessing information about websites. In particular, the DNS is what makes it possible to navigate the web using domain names like google.com instead of having to remember and use the underlying IP addresses for a given website, such as 172.217.3.206.