Keyword stuffing is a 'black hat' SEO technique that involves unnaturally overloading a webpage's content, meta tags, or back-end code with target keywords in a forced attempt to rank higher in search results.
Examples include repeating the same phrase unnecessarily (e.g., 'If you need a cheap plumber in Chicago, our cheap Chicago plumbers are the best cheap plumbers in Chicago'). Today, Google's advanced natural language algorithms heavily penalize websites that engage in keyword stuffing. Modern SEO relies on using keywords naturally and focusing on user intent and semantic relevance.