Domain & SEO Glossary: Key Terms Explained

How to Use This Domain and SEO Glossary

This glossary explains the terms most often encountered when researching, buying, rebuilding, monitoring, or selling a domain. Definitions are grouped by task so closely related concepts can be compared.

Some terms have formal definitions set by DNS standards, ICANN contracts, registries, or search-engine documentation. Others are product names or informal SEO shorthand. Where a term belongs to a particular provider—such as Domain Rating or Trust Flow—the provider defines the calculation and can change it.

Important distinction: A third-party SEO metric estimates something from that provider’s own crawl and model. It is not a Google score, a guarantee of rankings, or proof that a domain is safe to buy.

Domain Name and DNS Terms

Domain name: A human-readable name used within the Domain Name System, such as example.com. Registration provides contractual control for a period; it does not create permanent ownership in the same sense as physical property.
DNS (Domain Name System): The distributed system that associates domain names with records used to locate services and publish configuration. DNS can point web traffic, email, verification, and other services to different destinations.
TLD (top-level domain): The rightmost label of a domain name, such as .com, .org, or .domains. Generic TLDs and country-code TLDs can have different policies, eligibility rules, prices, and geographic meaning.
Second-level domain: The label immediately to the left of the TLD in a name such as example.com. Registration structures vary; in some country namespaces, registrants commonly register beneath an additional label such as example.co.uk.
Subdomain: A label beneath a registered domain, such as shop.example.com. The registrant normally creates subdomains through DNS; they are not separate registrar registrations.
Hostname: A domain name assigned to a network host or service. In everyday web work, people may say “domain” when they mean a hostname such as www.example.com.
URL (Uniform Resource Locator): The address of a specific resource, including a scheme and hostname and potentially a port, path, query, and fragment—for example, https://example.com/guides?id=7. One domain can contain many URLs.
Nameserver: A DNS server authoritative for a zone or delegated to answer for it. Changing registrar nameserver settings can move DNS management without moving the website files themselves.
DNS record: An entry within DNS. Common types include A and AAAA for addresses, CNAME for aliases, MX for mail routing, TXT for text and verification, and NS for delegation.
DNSSEC: Extensions that let resolvers validate signed DNS data and detect certain forms of tampering. DNSSEC does not encrypt traffic; HTTPS provides a separate layer for web connections.
Registry: The organization operating the authoritative registration database and policies for a TLD. A registry is not the same as the retail company through which a customer usually registers a name.
Registrar: An organization authorized to provide domain registration services for supported TLDs. It manages the customer account and communicates registration changes to the relevant registry.
Registrant: The recorded holder of registration rights and obligations for a domain. Accurate account, contact, payment, and recovery information are important for maintaining control.
RDAP: Registration Data Access Protocol, the structured protocol used to access available domain-registration data. Disclosure may be limited by privacy law, policy, and provider practices.
WHOIS: An older query-and-response protocol and a common informal name for registration-data lookup. WHOIS output is not a complete ownership history and privacy-redacted data is not inherently suspicious.
Authorization or EPP code: A credential commonly required to transfer a domain between registrars. Transfer procedures and exceptions depend on the TLD, status codes, and applicable policy.
Registry lock: An enhanced protection that requires an additional verified process for sensitive registry-level changes. It differs from the routine registrar transfer lock available in many accounts.

For the practical purchase and setup sequence, see How Domain Registration Works.

Domain Lifecycle and Acquisition Terms

Domain age: The time since a domain’s relevant registration date, although tools may derive it from registration data, first crawl, certificate, or archive evidence. Age alone does not confer authority or ranking value.
Expired domain: A registration whose paid term has ended. The former registrant may still be able to renew during part of the lifecycle, so “expired” does not necessarily mean available.
Redemption grace period: A registry lifecycle state in which a deleted registration may still be restored through the prior registrar, usually for an additional fee. Exact availability and timing depend on the TLD and provider.
Pending delete: A late lifecycle state generally preceding registry deletion. Restoration is normally no longer available once the name is in this state, but authoritative status data should be checked.
Dropped domain: A domain deleted from the registry and released for new registration. A drop can break continuity of control even if another party immediately registers the same string.
Aged domain: An informal marketplace term for a previously registered domain, often one that has remained continuously registered. It says nothing by itself about content, links, traffic, trademarks, or quality.
Backorder: A service request asking a provider to try to acquire a domain if it becomes available. A backorder is not a guaranteed purchase and multiple customers may compete through an auction.
Drop catching: The use of automated registrar connections to attempt registration immediately after deletion. Success depends on competition, registry behavior, provider access, and timing.
Domain auction: A sale process where qualified bidders compete under a platform’s rules. Expiry auctions, registry auctions, marketplace auctions, and private auctions can transfer different rights at different lifecycle stages.
Premium domain: A name priced above a registry’s or seller’s standard level. “Premium” describes pricing or inventory classification, not verified SEO value. Some registry-premium names also renew at premium prices.
Domain broker: An intermediary who may contact owners, negotiate, advise on pricing, or coordinate a sale. Confirm whom the broker represents, fee terms, authority, confidentiality, and conflicts.
Escrow: A transaction arrangement in which an independent provider holds funds or other assets until agreed conditions are met. Verify the provider and exact instructions independently because fake escrow sites and payment-redirection scams exist.
Account push: A change of domain control between accounts at the same registrar. It is distinct from an inter-registrar transfer and may have different locks, timing, and verification.
Registrar transfer: Movement of a registration from one registrar to another. A transfer does not inherently move DNS, hosting, content, analytics, or legal rights beyond the registration account.

The expired-domain guide explains the lifecycle without assuming every TLD follows the same timing.

Crawling, Indexing, and Search Terms

SEO (search engine optimization): Work that helps search engines understand content and helps people discover and choose a site through search. SEO does not guarantee inclusion, position, traffic, or revenue.
Search engine: A system that discovers, processes, and retrieves information in response to queries. Its crawler, index, ranking systems, and result presentation are related but distinct components.
Crawler: Automated software that requests web resources and follows discovery paths. Googlebot is Google Search’s crawler; other search engines and commercial tools operate separate crawlers.
Crawling: The process of requesting and fetching a URL. A successful crawl does not guarantee that the page will be indexed or shown for any query.
Indexing: Processing and storing information from a page for potential retrieval. An indexed page is eligible to appear but is not guaranteed impressions or a particular ranking.
Ranking: The ordering and selection of results for a particular search context. A page does not have one permanent universal “Google rank.”
SERP: Search engine results page. It can contain ordinary links, ads, images, videos, maps, rich results, and other features that vary by query, device, location, and time.
Search intent: The task or need behind a query, such as learning, comparing, navigating, or completing a transaction. Intent is an analytical model, not a fixed label supplied by Google for every keyword.
Keyword or query: A word or phrase used to describe a topic or a search. A query is what a person actually submits; “keyword” is often used for the topic targeted or measured by an SEO tool.
Impression: A recorded appearance of a result under a platform’s measurement rules. Definitions can differ between Search Console, advertising products, rank trackers, and analytics tools.
CTR (click-through rate): Clicks divided by impressions for the selected scope. Average CTR can hide large differences by query, position, device, country, and result type.
robots.txt: A file at a host’s root that communicates crawler access rules. It is not authentication, does not remove content already indexed, and should not be used to protect confidential information.
Noindex: A supported robots directive asking a search engine not to index a resource. The crawler must be allowed to fetch the URL to see the directive.
XML sitemap: A file listing canonical URLs a site wants search engines to know about, optionally with supported metadata. A sitemap assists discovery but does not guarantee crawling or indexing.
Canonical URL: The representative URL selected from a group of duplicate or substantially similar pages. A site can signal a preference, but Google may select a different canonical based on its evidence.
Redirect: A response or mechanism that sends a visitor or crawler from one URL to another. Permanent and temporary redirects communicate different intentions; redirect relevance and destination quality still matter.
HTTP status code: A response code such as 200 for a successful response, 301 for a permanent redirect, 404 for not found, or 410 for gone. A page can display an error message while incorrectly returning 200, creating a soft-404 situation.
Soft 404: A URL that appears to be missing, empty, or erroneous but does not return an appropriate not-found response, or is otherwise treated by a search engine as effectively missing.
Google Search Console: Google’s service for site owners to review Search performance, indexing information, sitemaps, manual actions, security issues, and URL Inspection data. It is more authoritative for Google-specific status than a third-party crawler, but still has reporting scopes and delays.
Manual action: An action shown in Search Console when a human reviewer at Google determines that pages or a site do not comply with spam policies. It is distinct from an algorithmic ranking change.

Link and Backlink Terms

Backlink: A link from another page to the page or site being analyzed. Counts vary by crawler coverage, canonicalization, redirects, duplicate pages, and whether historical links are included.
Referring domain: A domain or host containing at least one detected backlink. One referring domain may generate many links, so backlink count and referring-domain count answer different questions.
Anchor text: The visible text of a link. It helps people and search systems understand the destination, but artificial keyword repetition and ratio targets can indicate manipulation.
Link equity: Informal SEO shorthand for ranking value that may be conveyed through links. It is not a directly observable quantity, and third-party authority metrics do not measure Google’s internal treatment.
Dofollow link: Informal term for an ordinary link without a qualifying nofollow, sponsored, or ugc relationship. A rel="dofollow" value is not required.
Nofollow: A rel value used when other qualifications do not apply and the publisher would rather Google not associate with or crawl the destination from that link. Google treats it as a hint, not an indexing control for the target.
Sponsored: A rel value recommended by Google for ads, sponsorships, affiliate links, and other compensated placements.
UGC: User-generated content. rel="ugc" can identify links within comments, forum posts, and similar contributions.
Internal link: A link between URLs on the same site or property. Internal links support navigation, discovery, context, and site structure.
External link: A link to a different site. “External” describes destination ownership or hostname, not whether the link is good, harmful, followed, or sponsored.
Deep link: A link to a specific internal page rather than the homepage. Deep links can be especially important when evaluating which historical URLs attracted genuine references.
Sitewide link: A repeated link appearing across many pages through a common template, such as a footer or sidebar. Thousands of instances may represent one relationship rather than thousands of independent editorial choices.
Broken link: A link whose destination does not resolve to the intended useful resource. Causes include removed pages, malformed URLs, failed hosts, redirect errors, and changed ownership.
Link spam: Links created primarily to manipulate search rankings, including relevant examples described in a search engine’s spam policies. A low-quality link and a policy-violating link are related concerns but not automatically identical.
PBN (private blog network): A group of sites controlled or coordinated primarily to create links intended to manipulate rankings. A portfolio of legitimate sites is not automatically a PBN; purpose, independence, content, and link behavior matter.

A dependable audit goes beyond totals. Use the backlink-profile workflow to verify live source pages and link context.

Third-Party SEO Metric Terms

DR (Domain Rating): An Ahrefs metric estimating the relative strength of a target’s backlink profile on the provider’s scale. It is not a Google metric and should be interpreted with referring domains, source quality, history, and the provider’s current methodology.
UR (URL Rating): An Ahrefs page-level backlink metric. A domain-level score and a particular URL’s score are not interchangeable.
DA (Domain Authority): A Moz predictive metric calculated from its link data and model. Google does not use Moz Domain Authority as a ranking input.
PA (Page Authority): A Moz page-level predictive metric. Like DA, it belongs to Moz’s model rather than Google’s systems.
TF (Trust Flow): A Majestic metric based on how closely links connect to the provider’s seed set of trusted sites. It should not be described as Google trust.
CF (Citation Flow): A Majestic metric estimating link influence or quantity without being a direct quality measure. A TF/CF ratio is a derived diagnostic, not a universal pass/fail threshold.
Topical Trust Flow: Majestic’s categorization of link relationships into topic areas. It can help identify mismatches, but categories depend on the provider’s crawl and classification.
Spam Score or toxicity score: A provider-specific risk estimate based on its own signals. It is not a Google penalty notice and should be used to prioritize manual review of sources, patterns, and history.
Estimated organic traffic: A tool’s modelled estimate derived from tracked keywords, positions, search-volume estimates, and expected click behavior. It is not the site’s analytics total and can miss countries, queries, features, or recent changes.
Traffic value: An estimate of what modelled organic clicks might cost through paid search. It is not revenue, profit, an appraisal, or evidence that traffic will survive a domain change.
Keyword difficulty: A provider’s estimate of ranking competition, often weighted heavily toward backlink characteristics of current results. Definitions and scales differ, and the score may not capture content, brand, intent, SERP features, or business difficulty.

Compare calculations and limitations in the domain metrics guide.

Content and Technical SEO Terms

Title element: The HTML <title> for a page. Search engines may use it as one source for a result’s title link but can generate a different title.
Meta description: A page-level summary supplied in metadata. Google may use it for a result snippet when it describes the page well, but may instead select text from the page.
Heading: A structural heading from h1 through h6. Headings should organize content for readers; they are not slots that must be filled with every keyword variation.
Alt text: Text alternative supplied for an informative image. It should communicate the image’s relevant purpose or content; decorative images normally use an empty alt attribute rather than keyword stuffing.
Structured data: Machine-readable markup describing entities and page content, commonly using Schema.org vocabulary in JSON-LD. Valid markup can make a page eligible for supported features but does not guarantee them.
Core Web Vitals: A set of user-experience metrics currently centered on loading, responsiveness, and visual stability. They are one part of page experience, not a substitute for relevance and useful content.
Mobile-first indexing: Google’s use of the mobile version of a site’s content for indexing and ranking. Important content, links, metadata, and structured data should therefore be available in the mobile experience.
Hreflang: An annotation connecting localized versions of a page by language and optionally region. It is not a canonical directive and requires valid, reciprocal relationships.
Duplicate content: Identical or substantially similar content available at more than one URL. It is not automatically a spam violation, but can create unclear canonical signals and inefficient crawling.
Thin content: Informal shorthand for pages offering little unique or useful value for their purpose. Word count alone cannot determine whether a page is thin.
Orphan page: A page with no discoverable internal links from the site’s crawlable structure. A sitemap entry may aid discovery but does not replace useful navigation and context.

Domain History and Migration Terms

Web archive: A service preserving historical captures of public web pages. Captures can reveal former content and URLs but are incomplete and do not prove every version, owner, or date.
Historical URL: A URL previously used on a domain. Old URLs may retain links, bookmarks, citations, or harmful history and should be mapped before a relaunch.
URL mapping: A documented decision for each important old URL: restore equivalent content, redirect to a genuinely relevant destination, leave it gone, or investigate further.
Site migration: A substantial site change such as moving domains, protocols, platforms, content structures, or URLs. Migration work includes inventory, redirects, canonical signals, internal links, sitemaps, verification, and monitoring.
Redirect chain: A sequence where one URL redirects to another that redirects again. Chains add failure points and should usually be consolidated to a direct relevant destination.
Topical relevance: The degree to which the domain’s history, links, content, audience, and intended use meaningfully align. Relevance cannot be established from a keyword in the domain name alone.
Deindexed: Removed from a search engine’s index. A domain missing from results is not necessarily deindexed; it may be new, undiscovered, blocked, canonicalized elsewhere, low quality, or absent for a query-specific reason.

Before changing domains or rebuilding historical URLs, follow the site migration guide.

Terms Commonly Confused

Domain vs website

The domain is a registered name and DNS identity; the website is the content and software served at URLs on that domain.

A domain purchase does not automatically include hosting, content rights, analytics, email, or trademarks.

Registry vs registrar

The registry operates a TLD’s registration system; the registrar provides the customer-facing registration service.

A reseller may add another commercial layer without being the accredited registrar.

Crawling vs indexing

Crawling fetches a resource; indexing processes it for potential retrieval.

A URL can be crawled but not indexed, or known without a recent crawl.

Redirect vs canonical

A redirect sends the visitor elsewhere; a canonical preference can leave both URLs accessible.

Choose according to whether the alternate URL should remain available.

Expired vs dropped

Expired means the paid term ended; dropped means the registry deleted and released the registration.

Renewal or restoration may remain possible during earlier lifecycle stages.

Backlinks vs referring domains

Backlinks count detected link instances; referring domains group links by source domain.

A sitewide template can create many backlinks from one relationship.

Traffic estimate vs analytics

A tool models potential visits; analytics records measured activity under its implementation and consent rules.

Neither should be treated as automatically complete.

Metric vs penalty

A provider score is an estimate; a manual action is a Google-specific status reported in Search Console.

A falling third-party score does not prove a Google penalty.

Primary and Authoritative References

Bottom line: Precise language prevents expensive mistakes. Confirm whether a term describes DNS, registration, content, search processing, a provider’s metric, or a transaction step—and verify the underlying evidence before making a domain decision.