SEO involves optimizing a website to speak to search engines in a way that provides information about the site and aims to improve rankings. On-page SEO refers to on-site elements like titles, URLs, and content that can be optimized. Off-page SEO involves outside activities like link building, social media marketing, and social bookmarking. While link building is the most popular off-page technique, the quality of links matters more than quantity, and natural links from trusted sources are most valuable. Both on-page and off-page optimization are important for a successful SEO strategy.