Search engine optimization (SEO) is the process of increasing the quality and quantity of website traffic by increasing the visibility of a website or a web page to users of a web search engine. SEO refers to the improvement of unpaid results (known as "natural" or "organic" results), and excludes direct traffic/visitors and the purchase of paid placement. Primarily SEO pertains to search engine.
SEO may target different kinds of search, including image search, video search, academic search, news search, and industry-specific vertical search engines.
Optimizing a website may involve editing its content, adding content, modifying HTML, and associated coding to both increase its relevance to specific keywords and to remove barriers to the indexing activities of search engines. Promoting a site to increase the number of backlinks, or inbound links, is another SEO tactic. By May 2015, mobile search had surpassed desktop search.