Search Engines are the tools used to satisfy individual's intent. Like the one with Google, users tend to find the information they want with a query. It is with most of the Search Engines that happens to index the pages in different way and ranking them with the relevency with their important words (Keywords) density and frequency.
To begin with, different Search Engines have different ways using their Algorithms, list the pages on Search Engines when searched by the Users. This is more elaborated at Search Engine Watch Article.
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