Glossary of SEO terms: forty definitions in plain language, grouped by the job each one belongs to

SEO has around forty terms that come up in nearly every report, audit and agency call. They fall into six groups: how search engines find pages, how they decide the order, what you put on a page, links, technical checks, and measurement. Each definition below is one or two sentences, and where two terms get mixed up, the entry says which is which. Read it once from top to bottom, then keep it open next to your next audit. For the general marketing vocabulary around it, see sixty marketing terms in plain language.

How search engines find pages

Crawling. A program follows links and downloads pages. A page that is never crawled can never appear in results.

Googlebot. Google's crawler. Other search engines run their own, such as Bingbot.

Index. The stored copy of pages a search engine has processed and may show. Crawled and indexed are different: a page can be fetched and still left out.

Indexing. Processing a crawled page and adding it to the index.

Robots.txt. A text file at the top of a site that tells crawlers which paths they may fetch. It controls crawling, not whether a page appears.

Noindex. A tag that asks search engines to keep a page out of results. The page must be crawlable for the tag to be read.

Sitemap. A file listing the URLs you want crawled, with optional dates. It helps discovery and does not force indexing.

Crawl budget. How many pages a crawler will fetch from your site in a period. It matters on very large sites and rarely on small ones.

How the order is decided

Ranking. The position a page takes for a query. It changes by query, device, place and time.

SERP. Search engine results page. It now holds ads, maps, videos, answer boxes and AI summaries around the ten blue links.

Search intent. What the person typing wants: to learn, to find a site, to compare, or to buy. A page has to match the intent behind the words.

Keyword. A word or phrase people type into search. Better thought of as a topic with many phrasings, as our keyword research method shows.

Long tail. Longer, more specific queries with low volume each and clearer intent.

Keyword difficulty. A vendor's score for how hard a query is to rank for. Every tool computes it differently, so compare within one tool only.

E-E-A-T. Experience, expertise, authoritativeness and trust, the qualities Google's quality guidance asks reviewers to look for. It is a way of judging content, not a score.

Core update. A broad change to Google's ranking systems, announced on its status pages. Rankings move for many sites at once.

What goes on a page

Title tag. The page's headline in search results. Google may rewrite it, as its title link documentation explains.

Meta description. A summary in the page code that can appear under the title. It does not set rank.

Heading tags. H1 to H6, the outline of a page. Use one clear H1 and sub headings that describe each section.

Alt text. A short description of an image for people who cannot see it and for crawlers.

Canonical tag. A hint that says which URL is the main version when similar pages exist.

Structured data. Markup, usually JSON-LD, that labels facts on a page for machines. Schema.org defines the vocabulary.

Thin content. A page with too little original value to deserve a place. Merge or remove it.

Duplicate content. The same or nearly the same text on more than one URL. It splits signals between pages.

Links

Backlink. A link from another site to yours. One from a relevant, trusted site counts for more than many from unrelated ones.

Anchor text. The clickable words of a link.

Nofollow, sponsored, ugc. Link attributes that tell Google how to treat a link. Our page on the dofollow attribute explains all three.

Internal link. A link between two pages on your own site. It sets how authority and discovery flow, as the internal linking audit shows.

Domain authority. A third party score, first published by Moz, that predicts how well a site might rank. Google does not use it. See what it is and what it is not.

Link spam. Links created mainly to influence ranking, such as bought links or large scale exchanges. Google's spam policies list the patterns.

Technical checks

Core Web Vitals. Google's measures of loading, responsiveness and visual stability: largest contentful paint, interaction to next paint and cumulative layout shift. The web.dev guide defines each.

Mobile first indexing. Google mainly uses the mobile version of a page to index and rank it.

Redirect. Sending visitors and crawlers from one URL to another. A 301 marks a permanent move.

Status code. The server's reply to a request: 200 means fine, 404 not found, 5xx a server error.

Hreflang. Markup that tells search engines which language or country version of a page to show to whom.

Rendering. Running a page's code so the final content appears. Content that exists only after heavy scripts run is slower to process.

Measurement

Organic traffic. Visits that arrive from unpaid search results. How to measure and diagnose it is a separate page.

Impressions and clicks. Times a result was shown and times it was clicked, as reported in Search Console.

Click through rate. Clicks divided by impressions.

Search Console. Google's free tool showing queries, pages, indexing and errors for sites you verify. See its getting started guide.

Conversion. The action you count as success, such as a purchase or an enquiry.

The newest term: AI visibility

When a person asks an assistant instead of a search box, the answer may name a business, cite a page, or name no one. The words for this are still settling: AI visibility, answer engine optimisation and generative engine optimisation all describe the work of being named and cited in those answers. The old terms in this glossary still apply, because assistants read many of the same pages that search engines index. What changes is the thing you check. Rank is a position in a list. An assistant answer is a sentence that either contains your name or does not, and the same question can return different names on different days. AI Knows Us was built around that check: it asks ChatGPT, Gemini, Perplexity, Claude and Google AI Overviews the questions a buyer would ask and reports who they name.

Questions about SEO terminology

What is the difference between crawling and indexing?

Crawling is fetching a page. Indexing is storing and processing it so it can appear in results. A page needs both.

Are keywords and queries the same thing?

A query is what a person typed. A keyword is the phrase you target. Many different queries can lead to one page.

Is meta description a ranking factor?

No. It can affect clicks, because it may appear under your title in results.

Do I need to learn all forty terms?

Start with crawling, indexing, intent, title tag, backlink, internal link and impressions. They cover most conversations.

Where do new SEO terms come from?

Mostly from Google's own documentation and from tool vendors. Prefer the documentation when a vendor term conflicts with it.