Plain-language explanations for common DNS and lookup terms.
What is an RFC? RFC stands for Request for Comments. RFCs are published technical standards and guidance documents used to define how Internet protocols and systems behave.
Glossary
Jump to: @ (BIND Origin Shortcut), A Record, AAAA Record, Apex (Zone Apex / Naked Domain), Authoritative Nameserver, Cache Hit / Cache Miss, CNAME Exclusivity, CNAME Record, Derived Hostname Checks (Common Hostname Probes), DNS Trace, Glue Record, In-bailiwick, Mail Exchanger, MNAME (SOA), MX, MX Priority, Name Servers, NS Record, NXDOMAIN, Out-of-bailiwick, Public Suffix List (PSL), Recursive Resolver, Registrable Domain (eTLD+1), Registrar, RNAME (SOA), Root Hints, Root Servers, SOA, SPF / DKIM / DMARC, SRV Record, TTL, WHOIS / RDAP, Zone File (BIND Style)
| Term | Description | RFC / Standards |
|---|---|---|
| @ (BIND Origin Shortcut) | In BIND-style zone files, `@` refers to the current zone origin (the apex). Example: `@ IN A 192.0.2.10`. | RFC 1035 |
| A Record | Maps a hostname to an IPv4 address. | RFC 1035 |
| AAAA Record | Maps a hostname to an IPv6 address. | RFC 3596 |
| Apex (Zone Apex / Naked Domain) | The root of a domain zone (for example, `example.com` itself, not `www.example.com`). It is often called the naked domain or root domain. | RFC 1034, RFC 1035 |
| Authoritative Nameserver | A server that returns final DNS answers for a zone rather than recursively resolving names. | RFC 1034, RFC 1035 |
| Cache Hit / Cache Miss | A cache hit returns saved results quickly; a cache miss performs a fresh lookup and stores the result. | RFC 1034, RFC 1035 |
| CNAME Exclusivity | A DNS owner name with a CNAME record should not also have other record types at the same owner name. | RFC 1034, RFC 2181 |
| CNAME Record | Aliases one hostname to a canonical hostname. An owner with CNAME should not have other data types. | RFC 1034, RFC 2181 |
| Derived Hostname Checks (Common Hostname Probes) | A practical, predefined list of frequently used hostnames (for example `www`, `mail`, `autodiscover`) queried to discover likely records. This is a sampling mechanism and not a complete zone enumeration. | — |
| DNS Trace | Step-by-step lookup path showing how answers were obtained through authority chain and resolver attempts. | RFC 1034, RFC 1035 |
| Glue Record | Parent-zone A/AAAA records for in-bailiwick nameservers to prevent circular lookups. | RFC 1034, RFC 1035 |
| In-bailiwick | A nameserver hostname that is inside the same DNS scope as the zone it serves. | RFC 1034, RFC 1035 |
| Mail Exchanger | The hostname target in an MX record that accepts mail for the domain. | RFC 1035, RFC 5321 |
| MNAME (SOA) | Primary authoritative nameserver for the zone as specified in the SOA record. | RFC 1035 |
| MX | Mail exchanger records defining where email for a domain should be delivered. | RFC 1035, RFC 5321 |
| MX Priority | Preference value for MX targets; lower values are preferred first for SMTP delivery attempts. | RFC 5321 |
| Name Servers | Authoritative DNS servers published for a domain/delegation. | RFC 1034, RFC 1035 |
| NS Record | Delegates a zone to authoritative nameservers. | RFC 1035 |
| NXDOMAIN | DNS response code indicating the queried domain name does not exist. | RFC 1035 |
| Out-of-bailiwick | A nameserver hostname hosted outside the zone it serves. | RFC 1034, RFC 1035 |
| Public Suffix List (PSL) | A maintained list of domain suffix boundaries (for example `co.za`, `co.uk`) used to determine registrable domains. | — |
| Recursive Resolver | A DNS server that performs lookups on behalf of clients and returns cached or resolved answers. | RFC 1034, RFC 1035 |
| Registrable Domain (eTLD+1) | The effective top-level domain plus one label (for example `example.co.za`) often used for ownership grouping and related-domain logic. | RFC 8499 |
| Registrar | The accredited company through which a domain is registered and maintained. | — |
| RNAME (SOA) | Responsible party mailbox in SOA format, where the first dot represents `@` (for example `hostmaster.example.com.` -> `hostmaster@example.com`). | RFC 1035 |
| Root Hints | A bootstrap list of root server hostnames and IP addresses used by resolvers to begin iterative DNS lookups before cache is populated. | RFC 1034, RFC 1035 |
| Root Servers | The authoritative DNS servers for the root zone (`.`). They are the starting point for iterative resolution when finding top-level domain authority. | RFC 1034, RFC 1035 |
| SOA | Start of Authority record that describes key zone metadata such as serial, refresh, retry, expire, and minimum. | RFC 1035, RFC 2308 |
| SPF / DKIM / DMARC | DNS-based email authentication controls for sender authorization, signing, and policy. | RFC 7208, RFC 6376, RFC 7489 |
| SRV Record | Service locator record that maps a service/protocol pair to a target host and port with priority/weight. | RFC 2782 |
| TTL | Time To Live: how long resolvers may cache a DNS answer before refreshing it. | RFC 1035, RFC 2181 |
| WHOIS / RDAP | Domain/IP registration data sources; RDAP is the newer structured replacement. | RFC 3912, RFC 9082, RFC 9083 |
| Zone File (BIND Style) | A text file defining DNS records for a zone using directives such as `$ORIGIN` and `$TTL`, and records like SOA, NS, A, AAAA, MX, and TXT. | RFC 1035, RFC 2308 |