SEO glossary

Definitions for the key terms used throughout this guide, listed alphabetically. Each entry links to the chapter where the concept is covered in full.

A

Algorithm - The set of rules Google uses to decide which pages to rank and in what order. Google runs hundreds of algorithmic systems simultaneously, with major named updates - such as core updates and spam updates - periodically changing how certain signals are weighted. See: How ranking works.

Alt text - A written description of an image added in HTML. Used by screen readers for accessibility and by Google to understand image content. Relevant alt text can contribute to image search visibility. See: Image optimisation.

Anchor text - The clickable, visible text of a hyperlink. Google uses anchor text to understand what a linked page is about. Descriptive, varied anchor text pointing to a page strengthens its relevance signal for the topic covered. See: How to earn links.

B

Backlink - A link from one website to another. Backlinks from credible, relevant sources are one of Google's strongest ranking signals because they act as third-party endorsements of a page's authority and quality. See: Link building.

Bounce rate - In Universal Analytics, the percentage of sessions where a user viewed only one page and left. In Google Analytics 4, this is replaced by engagement rate - the inverse of sessions that lasted under 10 seconds with no conversion and no second page view. See: Key SEO metrics.

C

Canonical tag - An HTML element that tells Google which URL is the preferred version of a page when duplicate or near-duplicate versions exist. Prevents diluted ranking signals caused by the same content being accessible at multiple URLs. See: Canonicalisation.

Click-through rate (CTR) - The percentage of search impressions that result in a click. Calculated as clicks divided by impressions. A low CTR for a high-ranking page usually indicates that the title tag or meta description is not compelling enough. See: Key SEO metrics.

Content cluster - A group of pages organised around a central pillar page and a set of supporting sub-pages, each covering a related sub-topic. Internal links between cluster pages concentrate topical authority on the pillar. See: Content clusters.

Core Web Vitals - Three user experience metrics Google uses as ranking signals: Largest Contentful Paint (LCP, page load speed), Interaction to Next Paint (INP, interactivity), and Cumulative Layout Shift (CLS, visual stability). See: Core Web Vitals.

Crawl budget - The number of pages Googlebot will crawl on a site within a given timeframe. Large sites with many low-value pages may find important pages crawled less frequently because crawl budget is being spent on pages that add no ranking value. See: Crawl budget.

Crawling - The process by which search engine bots follow links across the web to discover new and updated pages. A page must be crawled before it can be indexed. See: Crawling.

D

Domain Rating (DR) - Ahrefs' proprietary score from 0 to 100 measuring the strength of a domain's backlink profile. Not a Google ranking factor, but a useful proxy for competitive benchmarking. Semrush's equivalent is Authority Score. See: Domain authority.

E

E-E-A-T - Experience, Expertise, Authoritativeness, and Trustworthiness. The framework Google uses in its Search Quality Rater Guidelines to assess whether content is produced by credible, knowledgeable sources. Trust is the most important element. See: E-E-A-T.

Engagement rate - In Google Analytics 4, the percentage of sessions lasting longer than 10 seconds, containing a conversion event, or involving two or more page views. Replaces bounce rate as GA4's primary session quality metric. See: Key SEO metrics.

F

Featured snippet - A block of content extracted from a ranking page and displayed above the organic results to directly answer a query. Winning a featured snippet requires clearly answering the question in a concise, well-structured passage. See: How ranking works.

I

Impressions - The number of times a page appeared in Google search results, whether or not it was clicked. Rising impressions with flat clicks indicate a CTR problem rather than a ranking problem. See: Key SEO metrics.

Indexing - The process by which Google stores and organises crawled pages in its database for retrieval in search results. A page must be indexed to rank. Pages can be excluded from the index intentionally (via noindex tag) or due to quality issues. See: Indexing.

Internal link - A hyperlink from one page on a site to another page on the same site. Internal links pass authority between pages, help Google discover content, and guide users through a site. See: Internal linking.

K

Keyword - A word or phrase that users type into a search engine. In SEO, keywords represent the topics you want your pages to rank for. See: Keyword research.

Keyword cannibalisation - When two or more pages on the same site target the same keyword, causing them to compete with each other for ranking. The fix is usually to consolidate or differentiate the pages. See: Keyword mapping.

Keyword difficulty (KD) - A score indicating how competitive it is to rank for a keyword, based primarily on the authority of pages currently ranking for it. Higher difficulty requires more backlinks and domain authority to compete. See: KD and search volume.

Keyword mapping - The process of assigning specific target keywords to specific pages on a site so every page has a clear focus and keywords are not duplicated across pages. See: Keyword mapping.

L

Link building - The practice of acquiring backlinks from other websites to improve a site's authority and rankings. Quality and relevance of linking sites matter more than quantity. See: Link building.

Long-tail keyword - A keyword phrase of three or more words, typically lower in search volume but higher in specificity and conversion intent. Long-tail keywords collectively account for the majority of all searches. See: Long-tail keywords.

M

Meta description - An HTML element that provides a brief summary of a page's content. Not a direct ranking factor, but influences click-through rate by appearing as the description text in search results. See: Title tags.

N

Noindex - An instruction placed in a page's HTML or HTTP header telling Google not to include the page in its index. Used legitimately to keep low-value pages out of search results, but damaging if applied to important pages by mistake. See: Sitemaps and robots.txt.

O

Organic traffic - Visitors who arrive at a site by clicking an unpaid search result. The primary measure of SEO effectiveness. See: Organic traffic analysis.

P

PageRank - Google's original algorithm for measuring page authority based on the number and quality of links pointing to it. No longer published publicly, but link-based authority signals remain a core part of Google's ranking systems. See: Domain authority.

R

Redirect (301) - A permanent redirect that forwards one URL to another, passing the majority of ranking signals from the old URL to the new one. Used when pages are moved or removed. A 302 redirect is temporary and does not reliably pass signals. See: Canonicalisation.

Referring domain - A website that contains at least one backlink pointing to your site. The number of unique referring domains is generally a stronger authority signal than total backlink count. See: Backlink audit.

Robots.txt - A text file at the root of a domain that gives crawl instructions to search engine bots - specifying which pages or directories they should or should not crawl. Blocking pages in robots.txt prevents crawling but does not remove them from the index if they are already indexed. See: Sitemaps and robots.txt.

S

Schema markup - Structured data code added to a page's HTML that helps Google understand content types - products, reviews, events, FAQs, recipes, and more. Correct schema can enable rich results in search, which increase CTR. See: Schema markup.

Search intent - The underlying goal behind a search query. The four main types are informational (learning), navigational (finding a specific site), commercial (researching before buying), and transactional (ready to act). Matching content to intent is one of the most important on-page factors. See: Search intent.

Search volume - The average number of times a keyword is searched per month. Used alongside keyword difficulty to assess whether a keyword is worth targeting. See: KD and search volume.

SERP - Search Engine Results Page. The page Google displays in response to a query, including organic results, paid ads, and SERP features such as featured snippets, image packs, local packs, and AI Overviews. See: How ranking works.

Site architecture - The way pages on a site are organised and linked together. A flat, logical structure allows Googlebot to reach all important pages within a few clicks and concentrates authority on key pages. See: Site architecture.

Sitemap (XML) - A file that lists the URLs on a site to help Google discover and prioritise them for crawling. Submitted via Google Search Console. See: Sitemaps and robots.txt.

T

Technical SEO - The set of optimisations that affect whether Google can effectively crawl, render, and index a site. Covers site speed, Core Web Vitals, HTTPS, site architecture, canonicalisation, sitemaps, and crawl budget. See: Technical SEO.

Title tag - An HTML element that specifies the title of a page. Appears as the clickable headline in search results and in browser tabs. One of the most important on-page SEO elements. See: Title tags.

Topical authority - The degree to which a site is recognised as a credible, comprehensive source on a specific subject area. Built by covering a topic deeply through clusters of interlinked content rather than isolated pages. See: Content clusters.

U

URL structure - The format and organisation of a page's web address. Clean, descriptive URLs that include the target keyword and reflect the site's hierarchy are preferable to long, parameter-heavy URLs. See: Site architecture.

W

YMYL (Your Money or Your Life) - Google's classification for content that could significantly affect a person's health, financial stability, safety, or wellbeing. Pages in this category are held to higher E-E-A-T standards, with particular scrutiny on author credentials and factual accuracy. See: E-E-A-T.