DNS

Domain Name System

The internet's phonebook -- maps domain names to IP addresses.

When you'd see it: Anytime a domain is set up, moved, or breaks. "It's a DNS issue" is a frequent diagnosis.

Why it matters: DNS translates human domain names into the IP addresses machines use. It is foundational plumbing, and because changes take time to propagate, DNS is a classic cause of "it works for me but not for you."