Words that degrade the quality of the page for search engines who classify it as being of low quality. These are usually words and phrases that trigger mistrust or loss of respect.  There is no exact list of poison words, but it is suspected that phrases like “buy PageRank” or “buy backlink”, terms related to gambling, politically incorrect terms and vulgar language can get your page buried in the SERPs, especially when used in the web page URL, title and description.