Cloaking is a SEO (Search Engine Optimization) technique. Basically it's about presenting the crawler of search engines a different website than normal users. Clocking is showing the search engine one thing and your visitors another. This method is treated as spam and is not recommended to use.
Cloaking is a search engine optimization (SEO) technique in which the content presented to the search engine spider is different from that presented to the user's browser. This is done by delivering content based on the IP addresses or the User-Agent HTTP header of the user requesting the page.
Cloaking refers to the practice of presenting different content or URLs to users and search engines. Cloaking is considered a violation of Google because it provides our users with different results than they expected. The cloaking is to boost a website's search engine rank on certain keywords.