Search engine optimization (SEO) refers to optimizing on-page and off-page ranking factors to achieve high search engine rankings. SEO is important because 85% of internet traffic comes from search engines, and users rarely view results past the first page. Search engines rank pages using algorithms that consider on-page factors like titles, headers, and content, as well as off-page factors like links and anchor text. Proper use of titles, meta tags, headings, images, URLs, and internal linking helps websites rank higher in search results.