DNS glossary | ClueDNS

Apex: The name at the top of a zone. It is the owner of that zone's SOA and authoritative NS RRsets. It may be below the root of the full DNS namespace.
Authoritative answer: An answer produced from authoritative data by a server authoritative for the relevant zone, normally indicated by the DNS AA flag. A cached copy from a recursive resolver is not an authoritative answer.
Authoritative server: A DNS server that serves authoritative data for one or more zones. Being named in delegation data does not by itself prove the server is reachable or correctly configured.
Bailiwick: The scope within which a nameserver's data is considered relevant or authoritative for a particular resolution step. Bailiwick rules limit which additional data a resolver accepts from a referral.
Canonical name: The target name stored in CNAME RDATA. The owner of the CNAME is the alias. “Canonical” here does not mean an HTTP canonical URL.
Child zone: A zone delegated from a parent zone. The parent publishes the delegation; the child publishes its own authoritative zone data.
Delegation: The parent-side NS data that transfers authority for a child namespace to named authoritative servers, with glue where required.
DNS host: The operator that serves a zone's authoritative DNS. It can be different from the registrar, registry, web host, and recursive resolver.
DNSSEC: DNS Security Extensions that let validating resolvers authenticate DNS data and denial of existence. DNSSEC does not encrypt ordinary DNS queries.
DS record: A parent-zone record containing a digest that identifies selected child DNSKEY material and connects the DNSSEC chain of trust.
Fully qualified domain name (FQDN): A domain name expressed relative to the DNS root. Zone-file notation commonly uses a final dot to make that root relationship explicit.
Glue: Address records included with a referral to make certain nameserver targets reachable, especially when their names are inside the delegated child. Glue is a role of A or AAAA data, not a separate RR type.
Label: One component of a domain name between dots. Inwww.example.com., www,example, and com are labels.
Negative caching: Caching of a negative result, such as NXDOMAIN or no data for a requested type, according to the response's negative-cache controls.
NODATA: Informal shorthand for a successful DNS response where the queried name exists but has no RRset of the requested type. It is different from NXDOMAIN.
NXDOMAIN: DNS response code indicating that the queried name does not exist in the responding namespace. It does not mean that a web page alone is missing.
Owner name: The domain name to which a resource record is attached. It is the first field in common presentation-format records.
Parent zone: The zone immediately above a delegated child. It controls the child's delegation NS and DS data, not the ordinary records inside the child.
Propagation: Informal operational language usually describing old cache expiry and independent refresh timing. DNS does not copy every change through one global propagation queue.
Recursive resolver: A service that obtains answers on a client's behalf, follows referrals, and normally caches results. Its response is an observation from that resolver at that time.
Referral: A response directing a resolver from a parent toward the authoritative servers for a delegated child zone.
Registrant: The person or organization holding the current registration rights for a domain name under the applicable registration agreement.
Registrar: The organization through which a registrant manages registration, renewal, transfer, contacts, and usually parent-side nameserver or DS settings.
Registry: The operator maintaining registration data and the authoritative zone for a top-level domain or another registration layer.
Resource record (RR): One typed DNS data item with an owner name, class, TTL, type, and type-specific RDATA.
Resource record set (RRset): All records with the same owner name, class, and type. Caches and DNSSEC signatures generally operate on the set, not an isolated line.
Root hints: Bootstrap names and addresses that let a recursive resolver begin contacting the DNS root server system. They are not a copy of the root zone.
Root zone: The zone at the top of the DNS hierarchy. It contains delegation data for top-level domains and is served by the root server system.
SERVFAIL: DNS response code indicating that a server could not complete the request. Causes can include DNSSEC validation failure, timeout, unreachable authority, or another processing problem.
Stub resolver: The client-side DNS component that sends queries to a recursive resolver rather than performing full iterative resolution itself.
Time to live (TTL): A value in seconds limiting how long a DNS result may be cached. It is not a promise that every cache keeps the result for exactly that long.
Zone: A coherently managed portion of the DNS namespace served as authoritative data. A zone is not necessarily the same thing as a registered domain.
Zone cut: The boundary where authority changes from a parent zone to a delegated child zone.

Primary terminology sources

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