A search engine is a software system that enables users to search for information on the internet by entering a query and receiving a ranked list of relevant results. At a technical level, search engines work through three core processes: crawling (discovering web pages using bots), indexing (analyzing and storing the content of those pages in a database), and ranking (ordering results based on relevance and quality signals when a user submits a query). Google dominates global search with approximately 90%+ market share, followed by Bing, Yahoo, Baidu (China), and Yandex (Russia).
How Search Engines Work
The crawling phase involves automated programs called spiders or bots following links from page to page across the web, collecting content as they go. The indexing phase processes that content — analyzing text, images, video, and structured data — and stores it in a massive database organized for fast retrieval. The ranking phase uses hundreds of signals to determine which indexed pages are most relevant and trustworthy for any given query: keyword relevance, backlink authority, page experience, content quality, user engagement, freshness, and many more. Google uses AI systems including RankBrain, BERT, and MUM to better understand query intent and match it to the best results.
Why It Matters for SEO
Understanding how search engines work is foundational to all SEO practice:
- Pages must be crawlable and indexable before they can rank — technical SEO ensures this
- Ranking signals inform every aspect of content, link building, and technical strategy
- Different search engines have different ranking factors (Bing favors exact match more, for example)
- The shift toward AI-powered ranking (RankBrain, BERT, MUM) has made intent-matching critical
- Search engines are evolving rapidly with AI-generated answers (AI Overviews) changing the traditional results page