An internet search engine is a software service that helps people find information online by discovering and organizing web content, then returning results it considers relevant to a query. It does not search every page on the live internet each time you enter a question; it retrieves results from material its systems have found and organized.
What is an internet search engine?
A search engine is a tool for finding information in response to a user’s query. It collects and organizes information about online content so it can retrieve likely matches when someone searches. The MDN Web Docs glossary likewise defines a search engine as a software system that searches for information on the web.
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A search engine is not the internet itself. It is an access point to content its systems have discovered and organized, and its results may include more than a list of links. Google’s explanation of how it organizes information describes the broader goal of making information useful and accessible through Search.
How does a search engine work?
A common way to understand web search is through three stages: crawling, indexing, and serving or ranking results. They describe a useful general model, not a guarantee that every web page passes through every stage.
1. Crawling and discovery
Automated programs, often called crawlers, discover URLs and visit pages they can access. They may find pages by following links from pages already known to them. A sitemap can also provide a crawler with a list of URLs. Google Search Central describes its own system as a fully automated search engine using web crawlers to explore the web and find pages to add to its index; that is Google’s description, not a formal definition of every search engine.
There is no single central registry of every web page. Technical barriers and site-owner settings can also limit a crawler’s access. Google’s guide to how Google Search works explains its process, while Search.gov’s overview of search-engine indexing cautions that engines do not necessarily crawl every page or index everything they crawl.
2. Indexing
After accessing content, a search engine can analyze and organize information about it in an index for later retrieval. Google describes its index as a database. Crawling a page does not guarantee that the page will be included: an engine may discover or visit a URL without adding it to its index.
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When someone submits a query, the engine looks for potentially useful matches in its index and selects and orders results using ranking systems. Google says its ranking can consider multiple signals, including the words in the query, a page’s relevance and usability, source expertise, the user’s location, and settings. These are examples of Google’s approach, not a universal formula shared by all providers. Google’s ranking-results explainer describes its system.
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Does a search engine search the entire internet?
No. An ordinary search query does not scan every page currently live on the web. The service can return only material available to its systems, and some pages may never be discovered, may not be accessible to its crawler, may not be indexed after crawling, or may not be selected for a particular query. As a result, being online does not guarantee that a page will appear in search results.
What is the difference between crawled, indexed, and ranked?
- Crawled: the engine’s crawler accessed or attempted to access a page.
- Indexed: the engine analyzed and stored information about the page for possible retrieval. Crawling alone does not ensure indexing.
- Ranked or served: the engine selected the page as a candidate for a query and placed it in the results according to its systems. Indexing does not guarantee that a page will appear for every query.
These distinctions explain why a page can be available on the web yet absent from results, or indexed but difficult to find for a particular search.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Are all search engines the same?
No. Providers may differ in the material they index, how they present results, the signals and controls they use, and how settings or location affect results. Public explanations from Google are useful examples of Google’s own process; they should not be treated as a precise account of every search service.
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