Cloaking is usually referred to domain name cloaking.  It means that when the search engine spiders visit your website, they are fed with manipulated data in order to rank high in SERP (Search Engine Ranking Pages) and the human visitors are shown different data so as to monitorize the website traffic. This method is considered a Black Hat method by search engines. For those of you who want to know more about cloaking here is a Q & A session straight from the cloaking software market leader Fantomaster.