SEO: terms A to Z
Every SEO term explained in plain English: keywords, backlinks, crawling, indexing, SERP, and more.
SEO has a reputation for jargon. This page cuts through it. Every term is explained the way you'd explain it to a smart friend who doesn't work in marketing.
A to C
| Term | Plain-English definition |
|---|---|
| Algorithm | The set of rules search engines use to decide which pages to show for a given search query, and in what order. Google's algorithm is constantly updated. |
| Alt text | A text description of an image. Helps visually impaired users and tells search engines what the image shows. See Image SEO & alt text. |
| Anchor text | The clickable, visible text of a hyperlink. E.g. in "read our SEO guide," the anchor text is "SEO guide." |
| Authority | A measure of how trustworthy and credible a website is in the eyes of search engines. Built through quality content and backlinks. |
| Backlink | A link from another website pointing to yours. Quality backlinks from reputable sites boost your authority. See Backlinks, explained. |
| Black hat SEO | Tactics that try to game search engine rankings through deception or manipulation. They break Google's spam policies, which can cost you rankings or get pages dropped. |
| Bounce rate | In GA4: the percentage of sessions that were not engaged, the exact inverse of engagement rate. In older Universal Analytics it meant something quite different: a visit to one page and out. Either way, a high figure may indicate the page is not meeting visitor expectations. |
| Breadcrumbs | Navigation links showing a visitor's location within a site hierarchy (e.g. Home > Blog > SEO). Also a structured data markup that appears in search results. |
| Canonical URL | The "official" version of a page when multiple URLs could show the same content. Prevents duplicate content issues. |
| Click-through rate (CTR) | The percentage of people who click your search result listing compared to how many see it. Higher CTR usually comes from compelling titles and meta descriptions. |
| Crawl | What search engine bots do when they follow links around the web and read page content to index it. |
| Crawl budget | The time and resources a search engine is willing to spend crawling your site. Google's guidance is aimed at very large or very fast-changing sites; if your pages get crawled soon after you publish them, you don't need to think about it. |
D to I
| Term | Plain-English definition |
|---|---|
| De-indexing | The removal of a page from search engine results. Can be accidental (noindex tag) or a penalty. |
| Domain authority (DA) | A score from 1 to 100, created by Moz, predicting how likely a site is to rank compared with competitors. Moz is clear it isn't a Google metric or a direct ranking factor: treat it as a comparison tool. |
| Duplicate content | Substantially identical content appearing at multiple URLs. Can confuse search engines about which page to rank. |
| E-E-A-T | Experience, Expertise, Authoritativeness, Trustworthiness. The qualities Google's systems look for in helpful content, and what its search quality raters are trained to assess. Google says E-E-A-T itself isn't a ranking factor, but the signals that line up with it do matter. |
| Featured snippet | A special result box near the top of Google search that answers a query directly, pulled from a single web page, with a link to the source. Search Console normally counts it as position 1, not "position zero." |
| Google Business Profile | Google's free business listing that appears in map results and local searches. See Google Business Profile for SEO. |
| Google Search Console | Google's free tool that shows how your site performs in search: clicks, impressions, indexing issues. See What is Google Search Console?. |
| Heading tags | HTML tags (H1, H2, H3…) that mark up headings in page content. H1 is the page's main title. Important for both readability and SEO. See Headings & content structure for SEO. |
| Impression | One instance of your page appearing in search results, whether or not anyone clicks on it. |
| Index | The search engine's database of web pages. If a page is "indexed," it can appear in search results. |
| Internal link | A link from one page on your site to another page on the same site. Helps search engines understand your site structure. See Internal linking explained. |
Crawling, indexing and ranking are three separate stages, and a page can quietly fail either of the first two. That is why having a page live on your site is not the same as having it in Google's index.
Read this as text
Everything you publish starts as a page on your site. Google works in three stages. First a crawler has to discover the page. Then Google decides whether to add it to its index, the database of pages it searches through. Only then, when someone searches, does Google rank the pages in its index based on hundreds of factors.
Pages can fall out at the first two stages. A page may never be crawled if nothing links to it and no sitemap has been submitted, if a robots.txt error blocks Google, or if the page loads very slowly. A page may be crawled and still be left out of the index if the content is thin, duplicated or low quality, if it carries a “noindex” instruction, or if Google couldn’t load it properly.
That is why having a page on your website doesn’t guarantee it’s in Google’s index, and a page that isn’t indexed won’t appear in search results at all.
J to O
| Term | Plain-English definition |
|---|---|
| Keyword | A word or phrase people type into search engines. Optimizing for relevant keywords helps you appear when they search. See Keywords, explained. |
| Keyword density | How often a keyword appears on a page relative to total word count. Less important today than it used to be: focus on relevance, not repetition. |
| Keyword research | The process of finding which words and phrases your potential customers search for. See Keyword research basics. |
| Keyword stuffing | Overloading a page with keywords in an unnatural way. Google treats it as a violation of its spam policies. |
| Knowledge panel | An information box Google shows for people, places, organizations, and things it already knows about, giving a quick snapshot of key facts. Google generates them automatically from sources across the web. |
| Link building | The practice of earning or acquiring backlinks from other websites to improve your authority. |
| Local SEO | Optimizing your website to appear in search results for geographically relevant queries: "plumber in Chicago." See Local SEO basics. |
| Long-tail keyword | A longer, more specific search phrase: "best accountant for freelancers in Seattle" vs. just "accountant." Less competitive, often higher purchase intent. |
| Meta description | A short summary you write for a page. Google builds the snippet under your title mainly from the page content, but sometimes uses your meta description instead when it describes the page better, so a good one can help click-through. See Page titles & meta descriptions. |
| Mobile-first indexing | Google primarily uses the mobile version of a page for indexing and ranking. See Mobile-friendliness & SEO. |
| Noindex | An instruction telling search engines not to include a page in their index. Used for private, duplicate, or low-value pages. |
| Off-page SEO | Optimization outside your website: backlinks, social signals, brand mentions. |
| On-page SEO | Optimization done directly on your page: titles, headings, content, images, internal links, URL. See On-page SEO explained. |
| Organic search | Unpaid search results. Visitors that arrive via organic search found you naturally, not through an ad. |
P to R
| Term | Plain-English definition |
|---|---|
| Page title | The HTML title of a page, shown in browser tabs. Google usually uses it for the blue title link in search results, but may generate a different one if it spots a problem with yours. One of the most important on-page SEO elements. |
| PageRank | Google's original system for ranking pages by how other pages link to them. Google says how it works has changed a lot since the early days, but that it's still part of its core ranking systems, alongside many other signals. |
| Penalty | A ranking demotion from Google, either from an algorithm update or manual action, usually due to policy violations. |
| Position | Where your page appears in search results: position 1 is the first organic result. |
| Redirect | Sending visitors (and search engines) from one URL to another. A 301 redirect passes SEO value to the destination. |
| Rich results | Enhanced search listings with extra visual detail: star ratings, event dates, recipes, product prices, breadcrumbs. Enabled by structured data markup. Google retired the FAQ rich result in May 2026, so FAQ markup no longer earns one. |
| Robots.txt | A file that tells search engine crawlers which pages or sections of your site not to crawl. See Sitemaps & robots.txt explained. |
S to Z
| Term | Plain-English definition |
|---|---|
| Schema markup | Code added to pages that helps search engines understand the content: business info, reviews, events, products. Enables rich results. |
| Search engine | A system for finding web pages: Google, Bing, DuckDuckGo. |
| SERP | Search Engine Results Page. The page you see after typing a query into a search engine. |
| Sitemap | A file, usually XML, listing the pages, videos, and other files on your site that you want search engines to know about, so they can crawl it more efficiently. See Sitemaps & robots.txt explained. |
| Slug | The URL-friendly text in a page address. Good slugs are short, descriptive, and keyword-relevant. |
| SSL/HTTPS | Google has described HTTPS as a lightweight ranking signal, carrying less weight than things like high-quality content. More importantly, browsers like Chrome flag sites without it as "Not secure." |
| Structured data | See Schema markup. |
| Technical SEO | Behind-the-scenes optimization: site speed, crawlability, indexing, mobile-friendliness, HTTPS. See Technical SEO basics. |
| Title tag | See Page title. |
| White hat SEO | Ethical, guideline-compliant SEO tactics focused on providing genuine value. The only approach worth taking. |
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