SEO refers to search engine optimization, which is the process of improving the visibility of a website in search engine results. SEO can provide huge targeted traffic at low or no cost. Effective SEO involves optimizing on-page elements like meta tags, headings, internal links, and keywords as well as off-page elements. Proper use of keywords, HTML elements, URL structure, and social media can help search engines understand and index a website better. Overuse of techniques like Ajax or images without text alternatives can hurt SEO. Choosing keywords strategically and optimizing the website layout, content, and code for search engines can help improve rankings and traffic from search.