SEO Terms Explained: The Plain-English SEO Glossary (2026)

SEO is full of jargon, and most glossaries explain one confusing term with three more. This one doesn’t. Each term gets a one-line definition in plain English, then a sentence on why it matters to you.

Last updated: 27 October 2026 · By Alan Spicer, YouTube Certified Expert

Part of the Website SEO series.

What does SEO mean?

SEO stands for search engine optimisation: the work of making your website show up higher in the free, unpaid results on Google and other search engines. It covers what you write, how your site is built, and how other websites link to you.

Organic results are the free listings on a search results page, as opposed to paid ads. SERP means search engine results page, the page you see after you search. Ranking or position is where your page appears on that page, with position one at the top. Search engine means any service that finds pages for a query; in the UK that’s mostly Google, with Bing behind it, and AI tools such as ChatGPT search increasingly in the mix.

On-page SEO is everything you control on the page itself: titles, headings, content and images. Off-page SEO is everything that happens elsewhere, mostly links and mentions. Technical SEO is how the site is built: speed, mobile layout, crawlability and structure.

Crawling and indexing terms

Google has to find, read and store your page before it can rank it. These terms describe that process.

If you’re launching a new site, my guide to getting your website on Google puts these into a step-by-step order.

Keyword terms

A keyword is the word or phrase someone types into a search engine. Every page should be built around one main keyword and the questions around it.

Search volume is the estimated number of times a keyword is searched each month. Keyword difficulty, often shortened to KD, is a 0 to 100 score estimating how hard it is to reach page one; each tool calculates it differently. Long-tail keywords are specific, lower-volume searches such as “seo for physiotherapists in leeds” rather than “seo”. They’re easier to rank for and usually closer to a purchase. Ahrefs found that almost 93% of the keywords in its US database get fewer than 10 searches a month, which is why long-tail content adds up.

Search intent is the reason behind a search. SEO tools label it four ways: informational (wants an answer), navigational (wants a specific site), commercial (comparing options) and transactional (ready to buy). Match the page to the intent or it won’t rank, however good it is.

Keyword cannibalisation happens when two of your pages target the same keyword and compete with each other. Seed keyword is the broad starting word you feed into a keyword tool. Keyword gap is the list of keywords your competitors rank for and you don’t.

Link and authority terms

A backlink is a link from another website to yours. Search engines treat good backlinks as votes of confidence, so they’re one of the strongest ranking signals, especially for competitive keywords.

Referring domains count the unique websites linking to you; 50 links from one site count as one referring domain. Anchor text is the clickable text of a link. Internal links point from one page on your site to another and help Google understand how your content fits together. Dofollow links pass ranking value; nofollow, sponsored and ugc links are tagged so they pass little or none. Affiliate links should carry the sponsored tag.

Domain authority is a generic name for third-party scores that grade a whole website’s strength. Moz calls its version Domain Authority; Semrush calls its version Authority Score, a 0 to 100 grade built from link power, organic traffic and spam signals. Google doesn’t use any of these scores; they’re shortcuts for comparing sites. Link spam means buying links or using schemes to manipulate rankings, which breaks Google’s spam policies.

Measurement terms

Impressions count how often one of your pages appeared in search results. Clicks count how often someone clicked through. CTR, click-through rate, is clicks divided by impressions. Average position is your mean ranking across all the searches a page appeared for. You’ll find all four in Google Search Console’s Performance report, which my Search Console guide explains.

Organic traffic is the visitors who arrive from unpaid search results. Bounce rate and engagement rate describe whether visitors interact with your page or leave. Conversion is any action you want a visitor to take, such as an enquiry, a sale or a sign-up. Core Web Vitals are Google’s measures of loading speed, responsiveness and visual stability.

Rank tracking means checking where your pages rank for chosen keywords over time, usually with a tool such as Semrush’s Position Tracking. Traffic estimates are a tool’s guess at another website’s visitors, worked out from rankings and search volumes. Treat them as rough comparisons.

Content and SERP feature terms

Featured snippet is the answer box Google sometimes shows above the normal results, quoting a short passage from one page. People Also Ask is the box of related questions that expand into short answers. Rich results are listings with extras such as stars, prices or FAQs, usually triggered by structured data, also called schema markup: code that describes your page’s content to search engines.

Pillar page is a long, broad guide on a core topic. Topic cluster is a group of shorter posts on subtopics that all link back to the pillar. Together they show search engines you cover a subject in depth. Evergreen content stays useful for years; thin content offers little value and often doesn’t get indexed. E-E-A-T stands for experience, expertise, authoritativeness and trust, the qualities Google’s quality guidelines look for in content.

AI search terms

AI Overviews are the AI-written summaries Google shows at the top of some searches, with links to the pages used. AI Mode is Google’s conversational search mode built on the same idea. Google says there are no extra requirements to appear in either: normal SEO best practice applies.

GEO, generative engine optimisation, is the newer name for making your brand show up in AI answers from ChatGPT, Gemini, Perplexity and Google’s AI features. AEO, answer engine optimisation, means much the same. AI visibility is how often AI tools mention or cite your brand for relevant prompts. A prompt is the question someone types into an AI tool, the AI equivalent of a keyword. LLM, large language model, is the type of AI behind these tools.

Tools now track this. Semrush’s AI Visibility toolkit and its Semrush One plans track brand mentions across ChatGPT, Google’s AI features, Gemini and Perplexity. My plain-English guide to Semrush explains how it fits alongside normal SEO data.

People also ask

Frequently asked questions

What is the difference between SEO and SEM?

SEO is earning free rankings in organic results. SEM, search engine marketing, traditionally means paid search ads, though some people use it to cover both paid and organic search.

What is a SERP?

SERP stands for search engine results page: the page you see after typing a search, including organic results, ads, AI Overviews, maps and other features.

What does indexed mean in SEO?

Indexed means Google has stored a copy of your page in its index and can show it in search results. A page that isn’t indexed can’t rank for anything.

What is a backlink in simple words?

A backlink is a link from someone else’s website to yours. Search engines treat links from relevant, trusted sites as a sign your page is worth ranking.

What is search intent?

Search intent is the reason behind a search: wanting an answer, a specific website, a comparison or a purchase. Pages rank best when they match the intent of the keyword they target.

What is GEO in marketing?

GEO, generative engine optimisation, is the work of getting your brand mentioned and cited in answers from AI tools such as ChatGPT, Gemini, Perplexity and Google’s AI features.

What is Authority Score in Semrush?

Authority Score is Semrush’s 0 to 100 grade of a website’s overall quality, based on its backlinks, organic traffic and signs of link spam. Google doesn’t use it, but it’s handy for comparing sites.