A search engine is software that crawls, indexes, and ranks web content, then returns an ordered list of results in response to a user's query. Google, Bing, and DuckDuckGo are the classic examples; by 2026 answer engines like ChatGPT, Perplexity, and Google's AI Mode perform much the same role.
Every traditional search engine does three things in sequence. Crawling: automated bots — see crawlers — follow links to discover pages. Indexing: the discovered content is parsed and stored in a vast database, organised by the words and entities it contains. Ranking: when someone searches, algorithms sift that index and order results by relevance, quality, and dozens of other signals, all in a fraction of a second.
The ten blue links are no longer the whole story. Google now assembles AI Overviews at the top of many results, synthesising an answer from several sources. AI Mode turns search into a back-and-forth conversation, and standalone answer engines skip the link list entirely, replying in prose with citations. Ask "what's the difference between HTTP and HTTPS" and a 2019 engine returned a list of articles; a 2026 engine drafts a two-paragraph explanation and cites three of them. The underlying crawl-index-rank machinery still runs — the presentation layer has been rewritten.
That shift is why visibility work now stretches beyond classic ranking into SEO that also earns citations inside AI answers.