Search engine optimization (SEO) is the process of improving the visibility of a website in organic search engine results. It involves optimizing on-page and off-page factors like keywords, content, links and social media to help search engines understand relevance and rank websites accordingly. The main goals of SEO are to increase qualified traffic and conversions by ranking high for targeted search terms. It is an ongoing process that requires understanding search engine algorithms and user behavior to maintain high rankings over time.