SEO, or search engine optimization, refers to techniques used to improve a website's rankings in organic search results. Properly optimizing a website can help drive free traffic and attract more relevant visitors. Historically, search engines like Yahoo, Google and Microsoft have evolved to rely on both on-page factors like keywords and content, as well as off-page factors including links and social mentions to determine a site's relevance and rank. While some black hat techniques exist, maintaining an ethical SEO approach through high-quality, keyword-optimized content is best for sustained success over time.