SEO, or Search Engine Optimization, is the practice of increasing the quantity and quality of traffic to a website through organic search engine results. It involves optimizing various aspects of a website, including its content, structure, and on-page elements like titles, meta tags, and URLs, to improve visibility and ranking in search engine results pages (SERPs). 

SEO also involves enhancing a site’s technical performance (like speed and mobile usability) and building backlinks from other sites to boost credibility and rank. The goal is to attract more relevant visitors to a site by ensuring it appears prominently for specific search terms.