Search engine optimization (SEO) is the process of growing 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 and the purchase of paid placement. Additionally, it may target different kinds of searches, including image search, video search, academic search,news search, and industry-specific vertical 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.