Search engine optimization (SEO) is the process of improving the visibility of a website in search engines through organic search results. SEO targets different types of search like image, local, video, academic, and industry searches. SEO is important because the majority of web traffic comes from major search engines like Google, Yahoo, and Bing. While SEO provides advantages like targeted traffic, increased visibility, and high return on investment, its disadvantages include a lack of control over algorithm changes and inability to compete against sites using unethical black hat SEO techniques.