SEO, or Search Engine Optimization, is a digital marketing practice that involves optimizing a website to increase its visibility in organic (unpaid) search engine results. The goal is to drive more high-quality traffic to a site by improving its ranking when users search for relevant keywords, products, or services. SEO involves a combination of tactics, such as on-page optimization (content and structure), off-page optimization (backlinks), and technical optimization (site speed and mobile-friendliness).