What do you mean by Cloaking?

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Cloaking is a search engine optimization (SEO) technique in which the content presented to the search engine spider is different from that presented to the user's browser. This is done by delivering content based on the IP addresses or the User-Agent HTTP header of the user requesting the page. When a user is identified as a search engine spider, a server-side script delivers a different version of the web page, one that contains content not present on the visible page, or that is present but not searchable. The purpose of cloaking is sometimes to deceive search engines so they display the page when it would not otherwise be displayed (black hat SEO). However, it can also be a functional (though antiquated) technique for informing search engines of content they would not otherwise be able to locate because it is embedded in non-textual containers such as video or certain Adobe Flash components. As of 2006, better methods of accessibility, including progressive enhancement, are available, so cloaking is no longer considered necessary by its proponents