There are many cloaking techniques, including IP based, User Agent based, and doorway pages. IP based cloaking detects the IP of a visitor, and if it’s a search engine spider, redirects it to an optimized, but not user-friendly page. User Agent based cloaking accomplishes the same thing, except that it differentiates between visitors according to the software they use to reach the site, since robots use their specific settings. Doorway pages are somewhat different. They are basically keyword-stuffed for search engines, but when a visitor reaches the page, it either redirects them immediately to another page, or requires them to click a link to “enter the site.” Keep away from cloaking, unless you want to be banned after a week of getting to the top.