Search engine
What is a search engine?
A search engine is software that discovers pages on the web, stores what it finds in a huge database called an index, and returns a ranked list of results when someone types a query. Google, Bing, Yandex, Baidu and DuckDuckGo are search engines; YouTube and Amazon run search engines for their own content.
Most web search engines work in the same three stages. A web crawler follows links and fetches pages (crawling). The engine processes each page, renders it, works out what it is about and stores it (indexing). When a query arrives, ranking systems pick and order the indexed pages that best match it, then display them on a SERP alongside ads and other features.
Not every search engine has its own index. Some build their results partly or wholly from another engine’s index; for example, Yahoo’s web results are powered by Bing. AI assistants with web search, such as ChatGPT search and Perplexity, also retrieve pages and then summarise them, which is why the line between search engines and answer engines is blurring.
Why search engine matters for SEO
SEO only exists because search engines decide who gets seen. Knowing how they find, store and rank pages tells you what to fix: a page that can’t be crawled can’t be indexed, and a page that isn’t indexed can’t rank, however good it is.
Google holds most of the search market in most countries, so SEO advice is usually Google-first. But Bing SEO matters too, partly because Bing’s index feeds other services.
How to check a search engine has your page
- Search for your exact page title in quotes, or use the site: operator, for example site:example.com/page. This is a rough check only.
- For Google, open the URL Inspection tool in Search Console. It tells you whether the URL is indexed and when it was last crawled.
- For Bing, use URL Inspection in Bing Webmaster Tools.
- If the page is missing, check for a noindex tag, a robots.txt block, a canonical pointing elsewhere or a lack of internal links to it.
Search engine FAQ
What is the most used search engine?
Google is by far the most used web search engine worldwide. Bing is second in many markets, and Baidu and Yandex are strong in China and Russia respectively.
Is ChatGPT a search engine?
Not in the classic sense, but ChatGPT search can look up the web and cite pages. It retrieves results and writes an answer rather than showing a ranked list of links.
Related SEO terms
Crawling is how search engines discover pages: automated bots fetch URLs and follow the links on them to find more pages.
Indexing is when a search engine analyses a crawled page and stores it in its index, so it becomes eligible to appear in search results.
A search algorithm is the set of systems a search engine uses to decide which indexed pages to show for a query and in what order.
Googlebot is Google’s web crawler. It fetches pages so Google Search can index them, using a smartphone crawler for most sites.
SERP (search engine results page)
A SERP (search engine results page) is the page a search engine shows after a query: organic links, ads, and features like snippets and maps.
Bing SEO is optimising a site to rank in Microsoft Bing, whose index also feeds other search services and AI tools.