Cloak: Something which hides, covers or keeps something else secret. (Cambridge Dictionary)
Cloaking: Also known as stealth, a technique used by some Web sites to deliver one page to a search engine for indexing while serving an entirely different page to everyone else. The search engine thinks it is selecting a prime match to its request based on the meta tags that the site administrator has input. However, the search result is misleading because the meta tags do not correspond to what actually exists on the page. Some search engines ... even ban cloaked Web sites. (Webopedia)
A good amount of web space has been dedicated to the merits of cloaking, but no one seems able to agree on the actual definition of the technique. One definition given is: "A technique used to deliver different web pages under different circumstances." This definition is too broad as page redirects for different browsers, for example, would be included under this definition but these pages are not hidden from search engine robots.
The one main characteristic of cloaking, according to Webopedia and Google, employs a different page delivered to search engines than the one displayed to visitors to the Web site; its only purpose being to hide content from search engines.
Many of those who employ cloaking techniques argue that they are presenting something different to a search engine rather than hiding something from it. The end result remains the same: the page presented to the search engine is different than the one anticipated by the visitor.