A Search engine is a database on the World Wide Web that helps us to quickly and easily find the web pages we want.
The user enters 'key words' or phrases on the subject that they are interested in. The search engine searches its database looking for references to the key words. It then returns web pages with links to the relevant websites it found.
The most popular or most visited websites are usually put near to the top of the results page.
Some examples of search engines are:
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Click on this link: Search Engine