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.
to trick the search engine. you show one thing to the search engine so it will show your website in the results for certain keywords but when a real user enter the site he will see different content.