Search Engine Basics

Search Engine Glossary

This search engine glossary explains more than 120 terms in plain words, from algorithm to zero-click search. Every definition is short enough to read in a few seconds, while each one links to the guide that covers it properly.

Updated 26 Oct 2026126 terms, A to ZSearchable
How to use it

Type any word into the search box below, or jump to a letter. Terms that appear on more than one guide link to the page that explains them in the most depth.

Usman AliWritten by Usman AliGrowth and SEO specialist · 7 years in SEO

A to Z

Search Engine Terms From A to Z

The list mixes core search engine terms with the SEO terms you meet once you start working on a site. Search it, or browse one letter at a time.

No term matches that search. Try a shorter word, or browse by letter.

A

AI crawler
A bot run by an AI company to collect pages for training models or for citing in AI answers. GPTBot and ClaudeBot are examples, each controllable through robots.txt. Web crawlers
AI Mode
A conversational search experience from Google that answers complex questions with a generated response, then lets you ask follow-ups. It splits your question into many smaller searches behind the scenes. AI search
AI Overviews
Short AI-written summaries that Google shows above some results, with links to the pages they draw from. They are built from pages already in Google's index. AI search
Algorithm
A fixed set of rules a computer follows to reach a result. In search, algorithms decide which pages match a query, then put those pages in order. Search engine algorithms
Algorithm update
A change to how a search engine scores pages. Small updates happen almost daily, while larger core updates can shift rankings across many sites at once. Algorithms
Alt text
A short written description attached to an image in the HTML. It helps screen reader users, while also telling search engines what the image shows. SEO basics
Anchor text
The clickable words in a link. Search engines read anchor text as a clue about the topic of the page being linked to. SEO basics
Answer engine
A search tool that replies with a written answer instead of a list of links. Perplexity or Google AI Mode work this way, citing the sources they used. Types of search engines

B

BERT
A language model Google added to Search in 2019 to understand the meaning of words in context. It helps with longer, conversational queries where small words change the meaning. Algorithms
Bing
Microsoft's search engine, the second largest worldwide by share. Its index also powers several partner engines plus a number of AI assistants. Best search engines
Bingbot
The crawler Microsoft uses to fetch pages for the Bing index. Genuine Bingbot visits come from addresses that resolve to search.msn.com. Web crawlers
Black hat SEO
Tactics that try to trick search engines rather than help users, such as hidden text or bought links. They break search engine guidelines, which can get a site penalised. SEO basics
BM25
A classic formula for scoring how well a document matches a query. It rewards pages that use the query words, while giving less weight to very common words or very long pages. Algorithms
Boolean operators
The words AND, OR or NOT used to combine search terms. They are most useful in library databases, although Google supports OR plus a minus sign for NOT. Search skills

C

Cache
A stored copy of something kept for quick reuse. Search engines cache pages or results so they can respond faster without fetching everything again. Components
Canonical URL
The preferred version of a page when the same content is reachable at several addresses. You can suggest it with a rel=canonical tag, although search engines make the final choice. Indexing
Click-through rate CTR
The share of people who click a result after seeing it. A result shown 100 times with 5 clicks has a CTR of 5%. What is a SERP
Cloaking
Showing search engines different content from what visitors see. It is a clear breach of Google's spam policies. SEO basics
Core update
A broad change to Google's main ranking systems, usually announced several times a year. It does not target one site, yet it can move rankings noticeably. Algorithms
Core Web Vitals
Three Google metrics for page experience: loading speed, responsiveness to input, plus visual stability while the page loads. They play a small part in ranking. Ranking
Crawl budget
The number of URLs a search engine is willing to crawl on one site in a given period. It matters mostly for very large sites. Crawling
Crawl rate
How many requests per second a crawler makes to a site. Search engines lower the rate if a server slows down or returns errors. Crawling
Crawler
Software that visits web pages automatically, saves them, then follows their links. It is also called a spider or bot. What is a web crawler
Crawling
The stage where a search engine downloads pages so it can read them. It comes after discovery but before indexing. What is crawling

D

Deindexing
When a page is removed from a search engine's index, so it no longer appears in results. It can be deliberate, through a noindex tag, or the result of a quality problem. Indexing
Disallow
A robots.txt rule that tells crawlers not to request certain paths. It controls crawling, not indexing, so a blocked URL can still appear if other sites link to it. Crawling
Discovery
The first stage of search, when an engine learns that a URL exists. Most discovery happens through links, sitemaps or IndexNow. How search engines work
DuckDuckGo
A privacy-focused search engine that does not build personal profiles of its users. It combines its own crawler with results from partner indexes. Best search engines
Duplicate content
The same or very similar text appearing at more than one URL. Search engines pick one version to show, which is why canonicals matter. Indexing

E

E-E-A-T
Short for experience, expertise, authoritativeness and trustworthiness. Google's quality raters use it to judge content, while ranking systems look for signals that reflect it. Ranking
Entity
A distinct thing a search engine can recognise, such as a person, place, company or idea. Understanding entities helps engines match meaning rather than exact words. Algorithms
Exact match
A search that only returns pages containing a phrase word for word. In Google, you get it by putting the phrase in quotation marks. Search skills

F

Forward index
A list that maps each page to the words it contains. Search engines turn it around into an inverted index, which maps each word to its pages. Indexing
Freshness
How recent a page's information is. Freshness matters a lot for news or prices, yet very little for timeless topics. Ranking

G

Google Search Console
Google's free tool for site owners. It shows which queries bring clicks, which pages are indexed, plus any crawling problems Google found. SEO basics
Googlebot
Google's main web crawler. Most of its crawling now uses a smartphone version, in line with mobile-first indexing. Web crawlers
Google-Extended
A robots.txt token that controls whether Google may use your content to train its Gemini models. Blocking it does not affect your rankings in Google Search. Web crawlers
Grounding
Tying an AI answer to real sources rather than the model's memory. Grounded answers cite the pages they used, which makes them easier to check. AI search

H

Hreflang
An HTML attribute that tells search engines which language or region a page is meant for. It helps the right version appear for each audience. SEO basics
HTTP status code
A three-digit number a server sends back with every page request. 200 means success, 301 means moved, 404 means not found, while 5xx codes mean a server error. Crawling

I

Index
A search engine's stored, organised copy of the pages it has processed. When you search, the engine looks through this index rather than the live web. Indexing
Indexing
The stage where a crawled page is analysed, then stored so it can be found. Not every crawled page gets indexed. Search engine indexing
IndexNow
An open protocol that lets websites notify search engines the moment a URL is added, changed or deleted. Bing, Yandex plus several other engines support it. Crawling
Information retrieval
The field of computer science behind search. It studies how to find the most relevant documents in a large collection for a given need. Components
Inverted index
A lookup table that lists every word alongside the pages that contain it. It is what lets a search engine answer queries in a fraction of a second. Indexing

J

JavaScript rendering
Running a page's scripts to see the content they produce. Google can render most JavaScript, although content that needs a click to appear may be missed. How search engines work
JSON-LD
A format for adding structured data to a page as a small block of code. Google recommends it because it sits apart from the visible HTML. SEO basics

K

Keyword
A word or phrase people type into a search engine. Site owners study keywords to understand what their audience is looking for. SEO basics
Keyword matching
Comparing the words in a query with the words in indexed pages. Modern engines go beyond exact matches to include synonyms or related meanings. Algorithms
Knowledge Graph
Google's large database of facts about entities and how they connect. It powers many quick answers on the results page. What is a SERP
Knowledge panel
The information box that appears beside results for well-known people, places or organisations. Its facts usually come from the Knowledge Graph. What is a SERP

L

Large language model LLM
An AI model trained on huge amounts of text to predict or generate language. LLMs power AI Overviews, chatbots plus many writing tools. AI search
Latent semantic indexing LSI
An information retrieval method from the late 1980s that found hidden links between words in a set of documents. Google has said it does not use LSI, even though the term still circulates in SEO. Algorithms
Local pack
The map with a short list of businesses that appears for local searches, such as coffee near me. Its order depends on relevance, distance plus prominence. What is a SERP
Long-tail keyword
A longer, more specific search phrase with fewer searches but clearer intent. An example is waterproof hiking boots for wide feet. SEO basics

M

Meta description
A short summary written in a page's HTML. Search engines may show it under the title in results, although they often write their own. SEO basics
Meta robots tag
An HTML tag that gives crawlers page-level instructions, such as noindex or nofollow. It only works if crawlers are allowed to fetch the page. Indexing
Meta search engine
A search engine that sends your query to several other engines, then combines their results. It does not keep an index of its own. Types of search engines
Mobile-first indexing
Google's practice of using the mobile version of a page for indexing plus ranking. If content is missing on mobile, Google may not see it at all. Indexing

N

Neural matching
An AI system Google uses to connect queries with pages that share meaning, even when the words differ. Algorithms
Nofollow
A link attribute that asks search engines not to treat a link as an endorsement. Google now treats it as a hint rather than a strict rule. SEO basics
noindex
A rule, set in a meta tag or HTTP header, telling search engines not to show a page in results. The page can still be crawled. Indexing

O

Off-page SEO
Work done outside your own site to build trust, mainly earning links plus mentions from other sites. SEO basics
On-page SEO
Improving a page's own content plus its HTML, including titles, headings and internal links. SEO basics
Organic search results
The unpaid listings a ranking system chooses, as opposed to ads that advertisers pay for. What is a SERP
Orphan page
A page with no internal links pointing to it. Crawlers struggle to find orphan pages unless they appear in a sitemap. Try it in the simulator

P

PageRank
The link-based scoring method Larry Page and Sergey Brin described in 1998. It treats a link as a vote, giving more weight to votes from important pages. Algorithms
Page experience
How pleasant a page is to use, including speed, mobile friendliness plus the absence of intrusive pop-ups. Ranking
People Also Ask
An expandable box of related questions that appears on many results pages. Each answer links to the page it came from. What is a SERP
Personalization
Adjusting results for an individual, for example by location or language. Google personalises far less than many people assume. Ranking
Position
Where a result appears on the results page. Position 1 is the first organic result below any ads or features. What is a SERP
Precision and recall
Two ways to measure search quality. Precision asks how many returned results are relevant, while recall asks how many relevant results were found. Components

Q

Query
The words a person types or speaks into a search engine to find something. Search skills
Query fan-out
A technique where an AI search tool splits one question into many related searches, then combines what it finds. AI search
Query processing
Everything a search engine does to understand a query before ranking, such as fixing spelling, spotting intent plus adding synonyms. Components
Quality rater guidelines
A public handbook Google gives to human raters who assess search quality. Their ratings help test changes, although they do not directly rank any page. Ranking

R

RankBrain
A machine learning system Google introduced in 2015 to interpret queries it had never seen before. Algorithms
Ranking
The stage that orders matching pages from most to least useful for a query. Search engine ranking
Ranking factor
Any signal a search engine uses when ordering results, such as relevance, links or page speed. Ranking
Redirect
An instruction that sends visitors plus crawlers from one URL to another. A 301 redirect is permanent, while a 302 is temporary. Crawling
Relevance
How closely a page matches what the searcher actually wants. It is the first thing ranking systems check. Ranking
Relevance scoring
Giving each candidate page a number for how well it matches a query. Formulas such as TF-IDF or BM25 are classic examples. Algorithms
Rendering
Running a page's code, including JavaScript, to see its final content as a browser would. How search engines work
Retrieval augmented generation RAG
An AI method that first retrieves trusted documents, then writes an answer based on them. It reduces made-up claims. AI search
Rich result
A search listing with extra visual detail, such as star ratings, prices or recipe times. Rich results usually depend on structured data. What is a SERP
robots.txt
A text file at the root of a site that tells crawlers which paths they may visit. Reputable bots follow it, while bad bots often ignore it. Crawling

S

Schema markup
A shared vocabulary from Schema.org used to label page content for search engines. It is the most common form of structured data. SEO basics
Search engine
A program that finds, stores and ranks web pages, then returns the most useful ones for each query. What is a search engine
Search intent
The goal behind a search, usually informational, navigational, commercial or transactional. Matching intent is one of the strongest ranking signals. SEO basics
Search operator
A special symbol or command that makes a query more precise, such as quotation marks or site:. Search skills
Search volume
An estimate of how many times a keyword is searched each month. It helps you judge demand before writing a page. SEO basics
Seed URL
A starting address given to a crawler. From seed URLs, the crawler follows links to discover the rest of the web. Web crawlers
SERP
Short for search engine results page, the page you see after running a query. What is a SERP
SERP feature
Any block on a results page beyond the standard blue links, such as a map, a video carousel or an AI Overview. What is a SERP
Snippet
The title, URL plus short description that make up one search result. What is a SERP
Soft 404
A page that looks empty or broken to a search engine yet still returns a 200 OK code. Google treats it like a missing page. Indexing
Spider
Another name for a web crawler, inspired by the image of a spider moving across a web of links. Web crawlers
Stemming
Reducing words to a shared root, so running or runs both match run. Indexing
Stop words
Very common words, such as the or of, that carry little meaning on their own. Indexing
Structured data
Code that labels what a page contains, such as a recipe, product or event. Google's case studies show it can lift click-through rates noticeably. See the case study

T

TF-IDF
Short for term frequency times inverse document frequency. It scores a word higher when it appears often in one page but rarely across the whole collection. Algorithms
Thin content
A page that offers little original value, such as a short page copied from elsewhere. Search engines may crawl it yet decide not to index it. Indexing
Title tag
The HTML element that sets a page's title. It usually becomes the clickable headline in search results. SEO basics
Tokenization
Splitting text into separate units, usually words, that an index can store. Indexing
Transactional query
A search made by someone ready to act, such as buy running shoes size 9. Uses of search engines

U

URL
The full web address of a page, such as https://searchenginebasics.tech/serp/. How search engines work
URL Inspection tool
A Search Console feature that shows whether Google has indexed a specific URL, plus the reason if it has not. Pipeline simulator
User agent
A short text label a browser or bot sends with each request to identify itself. Web crawlers

V

W

Web crawler
A program that requests web pages, saves a copy, then follows the links it finds to discover more pages. What is a web crawler
Web directory
A human-curated list of websites sorted into categories. Directories such as the Yahoo Directory led the early web before crawler-based engines took over. History of search engines
White hat SEO
Optimisation that follows search engine guidelines, focusing on helpful content plus a well-built site. SEO basics

X

X-Robots-Tag
An HTTP header that carries robots rules, such as noindex, for files like PDFs where a meta tag cannot be added. Indexing
XML sitemap
A file that lists the URLs a site wants crawled, often with the date each one last changed. Crawling

Z

Zero-click search
A search that ends without a click to any website, because the answer appears on the results page itself. What is a SERP

FAQ

Questions About Search Terms

What is a search engine glossary?

It is an alphabetical list of the words used to describe how search engines work, each with a short plain definition. This one also links every term to a full guide.

What is the difference between search engine terms and SEO terms?

Search engine terms describe how the system works, such as crawling or indexing. SEO terms describe what site owners do to perform well in that system, such as on-page SEO or link building.

Which terms should a beginner learn first?

Start with crawling, indexing, ranking, query and SERP. Those five words describe the whole journey of a page, while most other terms add detail to one of them.

Does Google use latent semantic indexing?

No. Google has said it does not use LSI, an older retrieval method from the 1980s. Modern systems such as BERT or neural matching understand meaning in far more advanced ways.

Is there a printable version?

Yes. The free search engine basics PDF includes a one-page cheat sheet with the 24 most important terms, ready to print for study or class.

Keep learning

Put the Terms Into Context

Definitions stick better once you see them in action. These pages show the same search engine glossary terms working together.

/Search engine basicsThe complete guide on one page./how-search-engines-work/How search engines workThe five stages, step by step./resources/how-search-engines-work-diagram/Search engine diagramEvery stage in one picture./tools/search-pipeline-simulator/Pipeline simulatorWatch the terms happen live./resources/search-engine-basics-pdf/Free PDF guideIncludes a printable cheat sheet./start-here/Start hereA reading path through every guide.
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