How to Use This Glossary

Domain terminology overlaps with DNS, networking, security, and trademark law. The terms here cover everything an owner is likely to encounter β€” from registration through transfer, security, and disputes. Use it as a reference; you do not need to memorize the whole thing.

Registration and Ownership

  • Domain name: The human-readable address used to reach a website or email server (e.g., example.com).
  • TLD (Top-Level Domain): The rightmost portion of a domain (.com, .org, .io). The broadest category.
  • SLD (Second-Level Domain): The portion immediately to the left of the TLD. In example.com, the SLD is "example."
  • gTLD (Generic TLD): Non-country TLDs (.com, .net, .info, .app).
  • ccTLD (Country-Code TLD): Two-letter TLDs assigned to countries (.uk, .de, .jp, .sa).
  • New gTLD: TLDs introduced after 2014 (.app, .dev, .shop, .blog).
  • Subdomain: A label to the left of the SLD (blog.example.com). Owned and managed by the domain owner.
  • Registry: The organization that operates a TLD. Verisign runs .com.
  • Registrar: A customer-facing company accredited to sell domains (Namecheap, GoDaddy, Cloudflare).
  • Registrant: The individual or organization that owns the domain registration.
  • ICANN: The Internet Corporation for Assigned Names and Numbers. Coordinates the global DNS root and accredits gTLD registrars.
  • Registration period: The duration of a registration, typically 1–10 years.
  • WHOIS: The public lookup service that returns registration info for a domain (registrant, dates, nameservers).
  • RDAP: The modern replacement for WHOIS. Returns the same data over a structured API.
  • Premium domain: A domain priced above standard registration fees due to perceived value (short, dictionary words, etc.).

DNS Fundamentals

  • DNS (Domain Name System): The global directory that translates domain names to IP addresses.
  • Nameserver (NS): A server that holds authoritative DNS records for one or more domains.
  • Authoritative nameserver: The nameserver designated as the source of truth for a domain.
  • Recursive resolver: A DNS server that performs lookups on behalf of clients and caches the results (Cloudflare 1.1.1.1, Google 8.8.8.8, your ISP).
  • Root zone: The top of the DNS hierarchy. Contains pointers to all TLD nameservers.
  • Zone file: The configuration file that contains all DNS records for a domain.
  • TTL (Time To Live): The number of seconds a DNS record may be cached. Lower TTLs mean faster propagation, more queries.
  • Propagation: The period during which DNS caches across the internet refresh after a change.
  • Glue record: An IP address provided alongside a nameserver delegation, needed when the nameserver itself is under the domain it serves (e.g., ns1.example.com for example.com).

DNS Record Types

  • A record: Maps a name to an IPv4 address.
  • AAAA record: Maps a name to an IPv6 address.
  • CNAME record: Aliases one name to another. Cannot exist at the apex of a domain.
  • MX record: Specifies which mail server handles email for a domain.
  • TXT record: Holds arbitrary text. Used for SPF, DKIM, DMARC, and verification tokens.
  • NS record: Identifies the authoritative nameservers for a domain or subdomain.
  • PTR record: Reverse DNS β€” maps an IP address back to a hostname.
  • SOA record: Start of Authority. Holds metadata about the zone.
  • SRV record: Specifies a host and port for specific services (XMPP, SIP, etc.).
  • CAA record: Certification Authority Authorization. Specifies which CAs may issue SSL certificates for the domain.
  • ALIAS / ANAME record: A non-standard CNAME-like record that works at the apex. Behavior varies by DNS provider.

Transfer and Lifecycle

  • Auth code (EPP code, transfer code): A per-domain secret required to initiate a transfer between registrars.
  • Transfer: Moving a domain from one registrar to another while retaining the same registration.
  • 60-day lock: ICANN policy preventing transfer for 60 days after registration or after a previous transfer.
  • Registrar lock (clientTransferProhibited): A registrar-set flag preventing outbound transfer until the owner unlocks.
  • Registry lock (serverTransferProhibited): A stronger lock enforced at the registry level. Typically requires phone authentication to remove.
  • Auto-renew: Setting that automatically charges the registrant for a renewal before expiry.
  • Grace period: Days after expiry during which renewal is still possible at standard pricing (typically 30–45 days).
  • Redemption period: Phase after the grace period during which the domain can be recovered with a high redemption fee (typically 30 days).
  • Pending delete: The 5-day window before an unrecovered domain returns to the available pool.
  • Drop catch: Registering a domain the moment it becomes available again after dropping.
  • Backorder: A pre-paid attempt to drop-catch a specific expiring domain.

Security and Validation

  • DNSSEC: DNS Security Extensions. Cryptographic signatures on DNS records to prevent forgery.
  • SSL/TLS certificate: A cryptographic credential binding a domain to a public key. Enables HTTPS.
  • DV (Domain Validated) cert: Cheapest tier; CA only confirms domain control.
  • OV / EV cert: Higher validation tiers verifying business identity.
  • Wildcard cert: Covers all single-level subdomains under a domain (*.example.com).
  • SPF (Sender Policy Framework): A TXT record listing servers authorized to send mail "from" your domain.
  • DKIM (DomainKeys Identified Mail): A cryptographic signature on outgoing mail proving the sender's authorization.
  • DMARC: A policy record telling receivers what to do with mail that fails SPF/DKIM checks.
  • HSTS (HTTP Strict Transport Security): Tells browsers to always use HTTPS for the domain.
  • Subdomain takeover: An attack where an unused CNAME pointing to a defunct service can be claimed by an attacker.

Disputes and Trademarks

  • UDRP (Uniform Domain-Name Dispute-Resolution Policy): ICANN's process for resolving trademark-related domain disputes.
  • Cybersquatting: Registering a domain matching a trademark with intent to sell or harm the rights-holder.
  • Typosquatting: Registering common typos of a popular domain to capture mistyped traffic.
  • Trademark Clearinghouse (TMCH): A central database of trademarks used during gTLD launches and post-launch claim notifications.
  • Sunrise period: A window before a new TLD's general availability when trademark owners can register matching names first.

Internationalization

  • IDN (Internationalized Domain Name): A domain containing non-ASCII characters (Arabic, Chinese, Cyrillic).
  • Punycode: The encoding that translates Unicode IDNs to ASCII for DNS transmission (xn-- prefix).
  • EAI (Email Address Internationalization): The standard supporting non-ASCII email addresses.

Marketplace and Investing

  • Aftermarket: The secondary market where domains are bought and sold between owners (Sedo, Afternic, Dan).
  • Domain auction: A bid-based sale of a domain, typically for premium or expiring names.
  • Appraisal: An estimated valuation of a domain, often produced by automated tools.
  • NameBio: A public database of historical domain sales prices.
  • Lease-to-own: A purchase structure where the buyer pays in installments and ownership transfers when fully paid.

Web3 (Adjacent)

  • ENS (Ethereum Name Service): Blockchain-based naming on Ethereum. Domains end in .eth.
  • Unstoppable Domains: A blockchain-based naming service supporting multiple TLDs (.crypto, .nft, .x).
  • Handshake (HNS): A decentralized root zone alternative.

The Reference

Bookmark this page. Most domain-related questions you will run into in the next several years come down to one of these terms β€” and once you can name the concept, the answer is a search away.