SEO stands for search engine optimization and refers to the process of getting traffic from organic search results on search engines like Google, Bing, and Yahoo. There are two main types of SEO: on-page optimization which involves factors controlled by the website owner like keywords, page speed, and descriptive URLs; and off-page optimization which involves external promotion methods like link building, social sharing, and article submissions to build reputation and backlinks. Proper on-page and off-page SEO techniques can help improve a website's ranking in organic search results.