What is a search engine?

A search engine is an information retrieval (IR) system for the world wide web. Users can enter keywords or phrases, submit them to the search engine and have a list of web pages returned that are relevant to the keyword or phrase entered.

Search engines gather their data in various ways but one of the most common is through the use of a web crawler, also known as a search engine spider or a search engine robot. These robots are programs that "visit" websites, read the information from each of the pages and then add it to the search engine index (database). Robots are constantly in operation on the web and can be seen in your web logs as they crawl through the links to index all of the information in your website.

Complex calculations are made on the information gathered by the crawlers to allow the search engine to categorise the web pages and determine which are the most important phrases and keywords. Once these calculations have been made the search engine database is ready for use.

It's a common misconception for people to think that search engines scour the depths of the internet every time a search is entered. Although a big part of a search engine's job is to do this it doesn't happen every time somebody searches for a keyword or phrase. The search engine provides access only to the information it has crawled.

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