It is an SEO technique but considered spam and for this reason, banned by search engines. When a web page is loaded with keywords or the keyword density crosses the permissible limit, it is termed stuffing by search engines and the web page is de-indexed from the search result pages.
It all started in the 1990s and soon became the favourite technique of achieving a high rank in a short time. But soon search engines noticed the SEO strategy and took strict measures to prevent SEOs from manipulating the web pages. Because search engines crawl websites to read the words that match with the search intents of users, webmasters try filling their sites with those words to become visible.
Keywords are stuffed in different ways like using synonymous, repeating words and hiding the keywords behind colours. It is like shouting at search engines to rank sites for specific keywords. There was a time when this technique was prevalent but it has become irrelevant today and using keywords beyond a specific limit is considered spamming.
What is the ideal keyword density of a page?
Google is quite strict with the sites that do spam with keywords. It strips the sites with overstuffed keywords of their search rank. Loss of rank results in loss of traffic that results in loss of business and profit in the long run. Today Google uses Artificial Intelligence to sense search intent of users and also to match search with results. It has many updates like Panda and Hummingbird to discourage webmasters from using spam SEO techniques.