If you look up the word "cloak" in a dictionary you will find a definition similar to the following:
- A loose outer garment, such as a cape.
- Something that covers or conceals: a cloak of secrecy.
Obviously in this case we're dealing with definition number two. Cloaking is concealment, concealment of the true nature of your site. By definition it is an underhanded technique.
Now sometimes a proponent of cloaking may label valid practice as cloaking in order to lend legitimacy to the practice, however not all of those things are cloaking. Serving a different page to a Netscape user is not cloaking. Using a cookie to offer a personalized experience on your website is not cloaking. Banning an IP address or email harvester from accessing your site is not cloaking. Changing your content depending on how it's accessed, such as automatically fetching the content related to the keywords someone searched on to find your site, is not cloaking.
Cloaking can be simply defined as serving different data to search engine spiders than what you serve to everyone else. It is the act of concealing your true content from the search engine in lieu of some other content, even if that other content is topically similar or identical. The technical requirements for cloaking are similar to the actions I listed above, however only when you are specifically targeting a search engine spider does it become cloaking. You see, whether or not you're cloaking depends more on why you're doing something, rather than how you're doing it.
Some people advocate cloaking, however I'm here to advise against it. I also hope to show you that you don't need to do it, and in fact most of the excuses people use when defending it are in fact worthless.
First I'd like to address to things that actually are cloaking:
Early on in the development of search engines they were not yet sophisticated enough to decipher what a page was about on their own, so they made wide use of meta tags until they realized that unscrupulous webmasters would try to trick them. Now however they are sophisticated enough and so very few still rely on meta tags in favor of running their own algorithms on a page's content to decide the topic. By cloaking you are in fact stepping back in time and telling the search engine what your site is about. The problem is you're probably lying, otherwise you wouldn't need to cloak. This really upsets the search engines and they have publicly stated that they will ban any site they catch cloaking. Think about how well your site would perform if Google permanently banned it. Is it worth the risk?