What is DNS and how does it work?

DNS (Domain Name System) translates human-readable domain names to IP addresses. Process: browser checks cache, then OS cache, then queries recursive resolver (ISP). Resolver queries root servers, then TLD servers (.com), then authoritative nameservers for the domain. Results are cached with TTL. DNS uses UDP port 53 (TCP for large responses or zone transfers). Records include: A (IPv4), AAAA (IPv6), CNAME (alias), MX (mail), TXT (text).