Domain & DNS terms, explained simply

A plain-English A–Z glossary of every domain name and DNS term you're likely to encounter, from A record to WHOIS.

Domain names and DNS come with a lot of technical vocabulary. This glossary explains every common term in plain English — no jargon required.

Quick summary

Use this glossary whenever you encounter an unfamiliar term in a guide, email, or conversation about your domain. Terms are listed A–Z. Click any term in the cross-links throughout the help center to come back here.

A record

A DNS record that maps a domain name to an IPv4 address. This is how your domain finds your website's server. For example, yourbusiness.com → 203.0.113.10. See DNS records explained.

AAAA record

Like an A record, but for IPv6 addresses — the newer, longer address format. Most hosting providers manage these automatically.

Apex domain

The root domain without any prefix. yourbusiness.com is the apex domain; www.yourbusiness.com is not. Also called "root domain" or "bare domain."

Auth code

See EPP code.

Auto-renew

A setting at your registrar that automatically renews your domain before it expires, charging your payment method on file. See Turning on auto-renew.

Authoritative nameserver

The nameserver that holds the official, definitive DNS records for a domain. When a DNS lookup is performed, the authoritative nameserver provides the final answer.

Bare domain

See apex domain.

CAA record

A DNS record that specifies which certificate authorities are allowed to issue SSL certificates for your domain. Adds a layer of security against fraudulent certificates. (The full name is written both "Certification Authority Authorization" in the IETF standard and "Certificate Authority Authorization" in some providers' docs — the record is the same either way.)

CNAME record (Canonical Name)

A DNS record that maps one domain name to another domain name (rather than to an IP address). Used for aliases and for connecting third-party services. See DNS records explained.

DKIM (DomainKeys Identified Mail)

An email authentication method that adds a cryptographic signature to outgoing emails, proving they're genuine and haven't been tampered with. Stored as a TXT record in DNS. See DKIM records, explained.

DMARC (Domain-based Message Authentication, Reporting & Conformance)

A DNS policy record that tells receiving email servers what to do when a message fails its DMARC check — which happens when neither SPF nor DKIM produces a pass matching the address in the From line. Options are none, quarantine, or reject. Also provides email abuse reports. See DMARC records, explained.

DNS (Domain Name System)

The global system that translates human-readable domain names (like yourbusiness.com) into numeric IP addresses that computers use to communicate. Often described as "the internet's phone book." See What is DNS?.

DNS propagation

The process by which a DNS change reaches DNS servers around the world. How long it takes depends on the record's TTL; for a nameserver change, registrars commonly quote 24 to 48 hours. See DNS propagation: why changes take time.

DNS record

An individual instruction stored in DNS that tells the internet something about your domain — where your website lives, who handles your email, etc. Common types include A, CNAME, MX, and TXT. See DNS records explained.

DNS resolver

A server run by your internet provider (or a public service like Google 8.8.8.8 or Cloudflare 1.1.1.1) that performs DNS lookups on your behalf when you visit a website.

Domain expiry

The date on which your domain registration ends. If it isn't renewed, the domain may pass through a grace period at your registrar, then a 30-day Redemption Grace Period once the registrar deletes it, then 5 days of pending delete — after which anyone can register it. See What happens when a domain expires.

Domain lock

See transfer lock.

Domain name

The human-readable address of a website, like yourbusiness.com. Registered at a domain registrar for a set term — ICANN says this is typically one to ten years — and it has to be renewed before the term ends. See What is a domain name?.

Domain privacy

A service that keeps the registrant's personal details out of the public registration record. ICANN describes two kinds: a privacy service leaves you listed as the registrant but publishes alternate contact details in place of yours, while a proxy service is itself listed as the registered name holder. Registrars market both as domain privacy; it's also called WHOIS privacy or private registration. See Domain privacy protection explained.

Domain registrar

A company that sells and manages domain name registrations. To sell generic extensions like .com it has to be accredited by ICANN. Examples include GoDaddy, Namecheap, Cloudflare Registrar, and Squarespace Domains.

Domain transfer

Moving a domain from one registrar to another. Requires unlocking the domain and obtaining an EPP/auth code. See How to transfer a domain.

EPP code (Extensible Provisioning Protocol code)

A password-like code required to authorize a domain transfer to a new registrar. Also called auth code, authorization code, or transfer code. See Unlocking a domain & getting the auth code.

Extension

See TLD.

Grace period

Properly the "auto-renew grace period": an optional window immediately after expiry in which your registrar still lets you renew. Each registrar sets its own length, so plan on about 30 days and never count on more; ICANN permits up to 45, and some registrars delete the domain straight away instead. A post-expiry renewal fee may apply. See What happens when a domain expires.

Host / Hostname

In DNS context, the "name" part of a record — the part before your domain. @ represents the root domain. www is the hostname for www.yourbusiness.com. mail is the hostname for mail.yourbusiness.com.

ICANN (Internet Corporation for Assigned Names and Numbers)

The non-profit organization that coordinates the global internet's naming systems, including domain name registration policies and the root DNS zone. Registrars selling generic extensions like .com have to be accredited by ICANN; accreditation for a country-code extension such as .uk comes from that country's registry instead.

IP address

A numerical label assigned to each device connected to the internet. IPv4 addresses look like 203.0.113.10. Your DNS A record maps your domain name to your server's IP address.

MX record (Mail Exchange)

A DNS record that specifies which mail server handles incoming email for a domain. Has a priority number — lower numbers have higher priority. See Email DNS records.

Nameserver

A server that holds the authoritative DNS records for a domain. When DNS looks up your domain, it queries your nameservers. Set at your domain registrar. See Nameservers vs DNS records.

NS record (Nameserver record)

A DNS record that specifies which nameservers are authoritative for a domain. These are set at your registrar and point to your DNS provider.

NXDOMAIN

A DNS response code meaning the name in the query does not exist. You see it when a domain doesn't exist or its DNS is misconfigured; browsers report it as a site they can't find.

Parked domain

A domain that is registered but not currently hosting an active website. May show a blank page, a registrar's ad page, or a placeholder. See Parked & redirected domains.

Propagation

See DNS propagation.

Registrant

The person or organization with the rights to a domain — ICANN's own policies call this the registered name holder. The registrant's contact details sit on the registration record, but most of them are now redacted rather than published, so a public lookup usually won't tell you who it is. Should always be the business owner, not a developer or agency. See Who owns your domain.

Registrar

See domain registrar.

Registry

The organization that manages a top-level domain (TLD). For example, Verisign manages .com. Registries set policies and pricing; registrars sell registrations to the public.

Redemption period

Properly the "Redemption Grace Period" (RGP): the 30 days that follow the moment your registrar deletes an unrenewed domain. ICANN requires every generic-extension registry to offer it, and during it only the registered name holder can restore the domain, through their registrar and usually for a restore fee. The domain can't be transferred during this window. See What happens when a domain expires.

Redirect

Automatically sending visitors from one URL to another. A 301 redirect is permanent; a 302 is temporary. See Parked & redirected domains.

Root domain

See apex domain.

SOA record (Start of Authority)

An internal DNS record automatically created by your DNS provider. It contains information about the zone and is managed automatically — you don't need to edit it.

SPF (Sender Policy Framework)

An email authentication DNS record (TXT type) that lists the mail servers authorized to send email from your domain. Helps prevent spoofing and improves email deliverability. See SPF records, explained.

SRV record (Service record)

A DNS record that gives the host and port for a specific service, such as internet calling (VoIP) or instant messaging.

SSL certificate

A digital certificate that enables HTTPS (encrypted) connections to your website. Most hosting providers issue SSL certificates automatically. Related to DNS in that the domain must point to your server before SSL can be issued. See What is SSL & HTTPS?.

Subdomain

A prefix added to a domain name to create a separate address. blog.yourbusiness.com and shop.yourbusiness.com are subdomains. See Subdomains explained.

TLD (Top-Level Domain)

The last part of a domain name — .com, .net, .org, .uk, .ca, and so on. Also called the "extension." Each one is managed by a registry. Some countries use a two-part ending like .co.uk, where .uk is the actual top-level domain and .co is a level below it.

Transfer lock

A security feature at registrars that prevents a domain from being transferred without authorization. Must be disabled before initiating a transfer. See Unlocking a domain & getting the auth code.

TTL (Time To Live)

A number (in seconds) that specifies how long DNS servers should cache a record before fetching a fresh copy. Lower TTL = changes spread faster. Higher TTL = fewer DNS queries and better performance. 3600 (1 hour) is a common default.

TXT record

A DNS record that holds arbitrary text information. Used for domain verification, SPF, DKIM, DMARC, and other purposes. See DNS records explained.

UDRP (Uniform Domain-Name Dispute-Resolution Policy)

An ICANN policy for resolving disputes over domain names, particularly abusive registrations that infringe a trademark. It can let a holder of trademark rights recover a domain from a squatter. Complaints are filed with one of ICANN's approved dispute-resolution service providers, not with ICANN itself. This is general information, not legal advice.

WHOIS

The original public directory of domain registration information. Since 28 January 2025 its replacement, RDAP (Registration Data Access Protocol), is the definitive source for generic extensions such as .com, and much registrant contact data is no longer published at all. Look up a domain with ICANN Lookup, which runs on RDAP. See Domain privacy protection explained.

WHOIS privacy

See domain privacy.

Wildcard DNS

A DNS record that matches any subdomain you haven't given a record of its own. For example, *.yourbusiness.com would match anything.yourbusiness.com. Often paired with a wildcard SSL certificate, which covers first-level subdomains such as shop.yourbusiness.com but not a deeper name like uk.shop.yourbusiness.com. See Subdomains explained.

Zone file

A text file containing all the DNS records for a domain. Many DNS providers let you export or import zone files. Useful for backing up your DNS before migrations.

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Domain & DNS terms, explained simply

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