SEO involves on-page optimization of a website and off-page activities to refine a site and improve search engine rankings. Key players in SEO include searchers, website owners, and search engines themselves. Properly implementing SEO can provide benefits like increased leads, higher conversion rates, and better results for local businesses. SEO involves both on-page techniques like optimizing content and structure, as well as off-page efforts like link building and social media marketing to boost rankings.