Cloaking is the practice of presenting different web page content to search engines than to human visitors. For example: a web page could display on search engines as promoting natural ways to boost energy, but when users click on the link they could be redirected to a page selling illegal drugs.
Google strongly opposes cloaking because it is a deceptive technique meant to manipulate search rankings by showing pages to Google that are optimized for bots rather than for genuine user experience.
Cloaking undermine's Google's aim to provide the most relevant and useful search results for queries.
By cloaking, sites are ranking higher in an artificial way that doesn't match the actual content users see. So Google penalizes sites caught using cloaking in order to better provide accurate, honest search results to people.