A program that allows a user to search for information stored on a computer system or network, most commonly the Internet. A web search engine uses programs called spiders or crawlers to regularly search the Internet, create copies of all pages and index them in a database. When a user queries this database by entering terms into the search engine, he or she will receive a list of web sites ranked by relevancy (as determined by the engine's algorithms). These are called organic listings. Many search engine databases also contain paid listings, which are typically purchased by commerce sites.