the Domain Name System
/ DNS spelled out: D-N-S /
People remember names; computers route by numbers. You type a name like www.example.com, but the routers that move your packets only understand numeric IP addresses such as 93.184.216.34. Something has to translate the name you remember into the number the network needs. The Domain Name System is that translator — often described as the Internet's phone book: you look up a name, and it gives you back the address. It is what lets you type a memorable name instead of memorizing a string of digits for every site you visit.
But DNS is not one big phone book in one place — it is a globally distributed, hierarchical database, queried billions of times a second, and held together by heavy caching. No single machine could answer all the world's lookups, so the namespace is split into a tree and the data is spread across many independent servers. A lookup walks down the tree: to resolve www.example.com, a resolver asks a root server (which knows where .com lives), then the .com servers (which know where example.com's servers are), then example.com's own authoritative server (which finally returns the address). Most of the time the answer is already cached nearby, so you never see this walk.
Why it matters: almost every Internet action begins with a DNS lookup — opening a web page, sending email, loading an app — so DNS is one of the most heavily used systems on the planet, and when it breaks, large parts of the Internet appear to break too. Be honest about its limits: classic DNS is by default unauthenticated and unencrypted, so answers can be forged or snooped, which is exactly why later additions like DNSSEC (signed answers) and DNS over HTTPS / DNS over TLS (private, encrypted queries) exist.
You click a bookmark for a news site. Before any page loads, your computer asks a DNS resolver, in effect: what is the IP address for www.example.com? The resolver returns 93.184.216.34, and only then does your browser open a connection to that numeric address.
Name in, address out — the lookup that precedes almost every connection.
DNS is not the web. The web (HTTP) is one of countless things that use names; email, apps, and updates all rely on DNS too. And DNS only resolves names to addresses — it does not fetch the page itself.