Cloaking

[Ruby707]

Cloaking is a black hat technique of SEO. When a website have two different instance for search engines and visitors then it is called cloaking.
That is essentially it, when you are serving different pages to the spiders and bots than you are to real users. Though it often goes further than that. Cloaking scripts would typically gene rate hundreds of thousands (if not millions) of fake pages on the fly which would then redirect back to one of your real pages for real users. However for bots, it would trick them into thinking your site was enormous, and loaded with pages about all sorts of keywords related to your niche.