SEO is a way of optimizing websites to be indexed by search engines so they can be found more easily. It involves analyzing sites and modifying them so search engines can read pages and prioritize them in results. While SEO has been used for years, it is especially important now as many sites rely on technologies search engines can't read. The document outlines what SEO is, how it works ethically through keywords and focusing pages, and unethical techniques to avoid like keyword stuffing, invisible text, and doorway pages which could get a site banned.