A web search engine is a software system that is designed to search for information on the world wide web. Many search engines use a form of boolean logic and truncation in the search. The functionality and results vary between search engines.

Crawler

A web crawler or spider is a computer program that automatically retrieves websites for use by search engines.
Examples of search engines that use this software include:
bing-100Bing google-100Google yahoo-100Yahoo

Meta search engines

A meta search engine uses software designed to optimise retrieval by querying multiple web search engines and combining the results.
Examples include:
isearchzoo-100Zoo infospace-100Infospace

Search the library here