Search Engine Definition

The World Wide Web has hundreds of millions of web pages available for user to do searches. The most common tool user do searches is the Web Search Engine (Internet Search Engine). Search engines help to minimize the time required to find information on all the websites avaible on the internet. Internet search engines are special sites on the web that are designed to help people find information stored on other websites.

Here are many definitions of a Search Engine:

On the Internet, a search engine is a co-ordinated set of programs which searches an index and returns matches to a specified keyword.
A directory of Internet content. If you're looking for specific information on the WWW, a search engine can list Web sites at which you'll likely find that information. Popular search engines include Live (MSN), Yahoo, Excite, Infoseek, etc.
A server (computer) or commonly a collection of servers dedicated to indexing internet web pages, storing the results in a giant database and returning lists of pages which match particular searched queries from within its database. The indexes are normally and automatically generated using spiders.
A software that searches for information and returns sites which provide that information. Examples of search engines are AltaVista, Google, Hotbot, Dogpile, etc.
An computerized index of the web pages; creating a searchable database. Example are AltaVista, Google, Live (MSN), etc.
A tool for searching information on the Internet by topic. Popular engines include InfoSeek, Inktomi (acquied by Yahoo) and Web Crawler.
A program that searches documents for specified keywords and returns a list of the documents where the keywords were found.
A program which acts like a card catalog for the Internet. Search engines attempt to help a user isolate desired information or resources by searching for keywords that the user specifies.
A tool or program that allows keyword searching for relevant sites or information on the Internet. For example: AltaVista, Dogpile, Google, Infoseek, Lycos and Yahoo are search engines.
A search engine is a type of software that creates indexes of databases or Internet sites based on the titles of files, keywords, or the full text of files. The search engine has an interface that allows you to type what you're looking for into a blank field.
A search engine is an application that searches for, and retrieves, data based on some criteria, especially one that searches the Internet for documents containing specified words.

How Web search engines work?

There are differences in the ways various search engines work, but they all perform three basic tasks:

They search the Internet -- or select pieces of the Internet -- based on important words.
They keep an index of the words they find, and where they find them.
They allow users to look for words or combinations of words found in that index.

Search engines work by storing information of web pages stored in computer machines that are connected to the internet called "Servers". These pages are retrieved by a computer "robot" program called "Web crawler" or "Spider". A website can exclude a web "robot" crawling through its website pages by using a text file called "robots.txt" that is stored in the directory of the website where the home (or index or default" page) is stored. The contents of each web page are then analyzed to determine how it should be indexed (for example, words are extracted from the titles, headings, or special fields called meta tags). The "robot" also analyze the content information of the web page to determine the relevancy of web page according to its Titles and Headings of the web page. The data about web pages are stored in an index database for use in later queries.

The dominant search engine giant - Google, store all or part of the source web page (referred to as a cache) as well as information about the web pages. The "cached page" stores the actual search text since it is the one that was actually indexed. When the content of the current page has been updated, a new "cached page" is being stored.

When a user enters a "Keyword" (example "stars") or "Key Phrase" (example "shooting stars") into a search engine, the search engine examines its index and provides a listing of best-matching website pages according to its criteria, usually with a short summary containing the web page´s title and sometimes parts of the content of the web page. Most search engines support the use of the boolean operators AND, OR and NOT to further specify the search query. Some search engines provide an advanced feature called proximity search which allows users to define the distance between keywords.

The usefulness of a "search" via a search engine depends on the relevance of the web pages it displays on the results of the search listing page. Since there are millions of webpages that include a particular word or phrase, some web pages may be more relevant, popular, or authoritative than others. Most search engines employ both standard search criteria and proprietary algorithm to rank the results to list the "best" results first. How a search engine decides which pages are the best matches, and what order the results should be shown in, varies from one engine to another and is proprietary to each search engine company its "secrete" closely guarded. Each search engine's methods also change over time as Internet usage changes, new techniques evolve to fight against abuses by some Search Engine Optimization (SEO) and Internet Marketing firms who uses "key word spamming" with the intend to fool the search engines.