DNS
Also known as: domain name system
The internet's phone book: it translates human-readable domain names into IP addresses.
When you type novablock.app into your browser, DNS turns that name into an IP address the network can route to. Every page load triggers many DNS lookups, one per domain the page references.
DNS is also a privacy choke point: your resolver sees every site you visit. Encrypted DNS (DoH, DoT) hides those lookups from the local network. DNS-level ad blockers (Pi-hole, NextDNS) work by refusing to resolve known ad and tracker domains for every device on your network.