Keyword stuffing is a SEO technique that involves the practice of “stuffing” content with keywords. Because the keywords are out of context or repetitive, they make little sense and provide no value for the search engine user.
Search engines consider keyword stuffing to be web spam and a black hat practice.
Google provides this example:
“We sell custom cigar humidors. Our custom cigar humidors are handmade. If you’re thinking of buying a custom cigar humidor, please contact our custom cigar humidor specialists at email@example.com.”