an authoritative name server

When you want the official answer about a domain — not a copy, not a guess, but the truth from the source — you ask its authoritative name server. It is the server that actually holds the master records for a zone and speaks for it. Like a city's own records office that issues the real birth certificate (as opposed to a photocopy a neighbor kept), an authoritative server is the original keeper of the facts for the names it is responsible for.

Concretely, an authoritative name server is the server (or set of servers) configured to serve a particular zone's data. When it answers a query for a name in its zone, it marks the reply as authoritative, meaning this is the source of truth. There are usually at least two for resilience: one primary that holds the editable master copy of the zone file, and one or more secondaries that pull synchronized copies via a zone transfer so the zone stays available even if one server is down. By contrast, the resolvers that ask on your behalf are not authoritative — they relay and cache answers but do not own them.

Why it matters: the authoritative server is where a domain's reality is defined. Change a record here — point www.example.com at a new IP — and that change is the new truth; it then spreads outward as caches expire. The bottom of every full DNS lookup is an authoritative server: the resolver walks root, then TLD, then arrives at the zone's authoritative server for the final answer. A common confusion is authoritative versus cached: an authoritative answer comes straight from the owner's server, while a cached answer is a saved copy held by a resolver that may be slightly out of date.