>The major search engines typically display three kinds of listings on their SERPs, Listings that have been indexed by the search engine’s spider, listings that have been indexed into the search engine’s directory by a human, and listings that are paid to be listed by the search engine.
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What is a Search Engine Results Page (SERP) ? | Webopedia
Domino's U.K. Uses Facebook, Foursquare to Drive Web Orders - ClickZ
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