Search Engines are web sites that direct the visitor to other web sites. Sometimes they are called indexes or directories. Essentially they are web pages that are tied into a very large database. This database contains a list of web sites that the search engine's spiders or bot's have crawled. They capture information about the web site's content, key words, images, and navigation structure.
The Search Engine business is dominated by a small number of firms including Google, Yahoo, and MSN. There are many others but they often rely on the shared technologies and databases.
Here is a list of the most common Search Engines.
www.google.com
www.yahoo.com
www.msn.com
www.alltheweb.com
www.altavista.com
www.lycos.com
www.hotbot.com
www.webcrawler.com
www.mamma.com
www.ask.com
www.ditto.com