SEO (Search Engine Optimization) is the process of optimizing website content to increase organic search visibility and traffic. It involves technical, on-page, and off-page optimization. Technical optimization focuses on website speed, structure, and indexing. On-page optimization involves headings, keywords, meta tags, images, and internal/external links. Off-page optimization uses link building and social media to improve search rankings. Free SEO tools can help with optimization, keyword research, and analysis.