SEO Glossary — Every Term You Need to Know
SEO has a lot of jargon. This glossary explains the most important terms in plain English — no assumed knowledge, no abbreviations left unexplained.
A–C
- Algorithm
- The set of rules and signals Google uses to rank pages. Google runs hundreds of algorithms simultaneously; when people say "a Google algorithm update", they mean Google changed the weighting of some of these signals.
- Anchor text
- The visible, clickable text of a hyperlink. Anchor text tells Google what the linked page is about. "Click here" is weak; "best keyword research tools" is descriptive and useful.
- Backlink
- A link from another website to yours. Backlinks are one of Google's most important ranking signals — they act as votes of confidence from other sites.
- Canonical tag
- An HTML element that tells Google which version of a page is the "preferred" one when duplicate or near-duplicate versions exist. Prevents duplicate content from diluting your rankings.
- Crawl budget
- The number of pages Googlebot will crawl on your site within a given time period. Large sites with thin or duplicate content can exhaust their crawl budget before Google reaches important pages.
- CTR (Click-Through Rate)
- The percentage of people who see your result in search and click on it. CTR is calculated as (clicks ÷ impressions) × 100. Higher CTR generally correlates with better rankings over time.
D–K
- Domain Authority (DA)
- Moz's proprietary 0-100 score estimating how authoritative a domain is. Not a Google metric — a tool-specific estimate based on backlink data.
- Domain Rating (DR)
- Ahrefs' version of domain authority. Also 0-100, based on the strength of a domain's backlink profile relative to all other sites in Ahrefs' index.
- Featured snippet
- A boxed result at the top of Google's results that answers the query directly — sometimes called "Position Zero". Winning a featured snippet significantly increases CTR.
- Index
- Google's database of web pages. A page must be indexed to appear in search results. Being crawled doesn't guarantee being indexed.
- Keyword difficulty (KD)
- A 0-100 score estimating how hard it would be to rank on the first page for a given keyword. Each tool calculates it differently — always validate with a manual SERP check.
L–R
- Long-tail keyword
- A keyword phrase of 4+ words with lower search volume but more specific intent and lower competition. Most SEO traffic comes from long-tail keywords.
- Noindex
- A directive in a page's HTML that tells search engines not to include that page in their index. Useful for thin pages, admin pages, and duplicate content — catastrophic if accidentally applied to important pages.
- Organic traffic
- Visitors who arrive at your site by clicking an unpaid search result. Distinct from paid traffic (Google Ads), referral traffic (links), and direct traffic (typing your URL).
- Page authority
- Moz's metric for the authority of an individual page (as opposed to the whole domain). Useful for assessing how strong specific competitor pages are.
- Referring domain
- A unique website that links to your site. 50 links from 50 different referring domains is much stronger than 50 links from one domain.
- Robots.txt
- A file at the root of your website that tells search engine crawlers which pages or sections they're allowed to crawl. Accidentally blocking important sections is a common technical SEO mistake.
S–Z
- Schema markup
- Structured data code added to pages to help search engines understand the content type. Enables rich results like star ratings and FAQ dropdowns in SERPs.
- Search intent
- The underlying goal behind a search query. Intent categories: informational (want to learn), navigational (want to find a specific site), commercial (researching to buy), transactional (ready to buy). Matching content to intent is essential for rankings.
- Sitemap
- An XML file listing all the pages on your site that you want search engines to crawl and index. Submitting a sitemap to Google Search Console speeds up discovery of your pages.
- Topical authority
- Google's assessment of how comprehensively a site covers a topic area. Sites with deep, well-organised content on a specific niche are rewarded with higher rankings across all keywords in that niche.
- Zero-click search
- A search query that Google answers directly on the results page — via a featured snippet, knowledge panel, or People Also Ask box — without the user clicking through to any website. Growing in prevalence as AI Overviews expand.