Search engine optimization is the process of increasing the quality and quantity of website traffic by increasing the visibility of a website or a web page to the user of a web search engine.
SEO refers to the improvement of unpaid results and excludes direct traffic/visitors and the purchase of paid placement.
SEO may target different kinds of search, including image search, academic search, news search, and industry-specific vertical search engine.
Optimizing a website may involve editing its content, adding content, and modification HTML and associated coding to both increase its relevance to specific keywords and 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.

As an internet marketing strategy, SEO considers how search engine works, the computer-programmed algorithms that dictate search engine behavior what people search for, the actual search terms of keywords types into search engines, and which search engine are preferred by their targeted audience. SEO is performed because a website will receive more visitors from a search engine the higher the website ranks in the search engine results page. Their visitors can then be converted into customers.
SEO differs from local search engine optimization in that the latter is focused on optimizing a business online presence so that its web pages will be displayed by the search engines when a user enters a local search for its products or services. The former instead is more focused on national or international search.

History
Webmasters and content providers began optimizing the website for search engines in the mid-1990s, as the first search engines were cataloging the early web. Initially, all webmaster only needed to submit the address of page , or URL, to the various engines which would send a “spider ” to “Crawl” that page, extract links to other page from it, and return information found on the page to be indexer, extracts information about the page, such as the words it contains, where they are located and any weight for specific words, as well as all links the page contains. All of this information is then placed into a scheduler for crawling at a later date.