DNS (Domain Name System) is the internet's distributed name-resolution system that translates human-readable domain names (example.com) into machine IP addresses (93.184.216.34).
It's a hierarchically distributed global database and the first step a browser takes to learn which server to connect to.
Resolution is hierarchical: a resolver asks the root, then the TLD (.com), then the authoritative nameserver to get the final IP, caching each step's result for its TTL to reduce repeat lookups. Common record types include A (IPv4)/AAAA (IPv6), CNAME (alias), MX (mail), TXT (verification/policy), and NS (nameserver). A longer TTL improves cache efficiency but slows propagation of changes — a trade-off.
DNS is more than translation; it's a traffic-control tool. GeoDNS returns a nearby IP, DNS round-robin rotates through multiple A records, and anycast makes DNS the front door of CDNs and load balancing. On security, plaintext DNS is vulnerable to eavesdropping and tampering, so it's encrypted via DoH (DNS over HTTPS)/DoT and signed with DNSSEC to prevent response forgery. The host portion of a URL is exactly what DNS resolves.