What is search engine?????

• Search engine is a computer application that retrieves documents or files or data from a database or from a computer network (especially from the internet). 

• A tool designed to search for information on the World Wide Web.

• An application that searches for, and retrieves, data based on some criteria, especially one that searches the Internet for documents containing specified words.

• A website that allows you to search the Internet for a specific topic.

• The software that searches an index and returns matches. Search engine is often used synonymously with spider and index, although these are separate components that work with the engine.

• A program that indexes documents, then attempts to match documents relevant to the users search requests

• A web site that offers its visitors the ability to search the content of numerous web pages on the Internet. Search engines periodically explore all the pages of a website and add the text on those pages into a large database that users can then search. With a search engine, publishing web pages that incorporate relevant key phrases, prominently positioned in particular ways, is critical. Contrast this with directories, which don't siphon content out of the HTML of a site's constituent pages, but instead are comprised solely of site names and descriptions written or edited by human reviewers

• A program which acts as a card catalog for the Internet. Search engines attempt to index and locate desired information by searching for keywords in which a user specifies. The method for finding this information is usually done by maintaining indices of Web resources that can be queried for the keywords entered by the user. These lists are either built from specific resource lists (as is the case with a search directory) or created by Web programs, with insect names like bots, spiders, crawlers, and worms.

example :
www.google.com
www.alltheweb.com
www.altavista.com
www.yahoo.com
www.imhalal.com
www.dogpile.com
www.ask.com
www.gigablast.com
www.msn.com
www.lycos.com
www.scirus.com
www.duckduckgo.com
www.dmoz.com
etc.