Search engine optimization involves optimizing websites to increase their visibility in search engines. There are two main types of search engine results - paid search results that appear due to advertising and organic search results that are determined by relevancy. To rank highly in organic search results, websites must focus on both onsite and offsite optimization. Onsite optimization involves optimizing on-page elements like titles, meta descriptions, internal linking, and keyword usage. Offsite optimization involves factors like the quality, number, relevancy and age of external links to the site.