Search engine optimization (SEO also search optimization) is the process of editing and organizing the content on a webpage or across a website to increase its potential relevance to specific keywords on specific search engines and importantly ensuring that external links to the site are correctly titled and in abundance. This is done with the aim of achieving a higher organic search listing and thus increasing the volume of targeted traffic from search engines.

SEO is one of the key Web Marketing activities and can target different kinds of searches, including image search, local search, and industry-specific vertical search engines.

SEO considers how search engines work and what people search for. Optimizing a website primarily involves editing its content and HTML coding to both increase its relevance to specific keywords and to remove barriers to the indexing activities of search engines. Sometimes a site's structure (the relationships between its content) must be altered too. Because of this it is, from a client's perspective, always better to incorporate Search Engine Optimization when a website is being developed than to try and retroactively apply it.

Another class of techniques, known as black hat SEO or Spamdexing, use methods such as link farms and keyword stuffing that degrade both the relevance of search results and the user-experience of search engines. Search engines look for sites that employ these techniques in order to remove them from their indices.

The term 'Search engine friendly' refers to a website that has been search optimised.

History

According to industry analyst Danny Sullivan, the earliest known use of the phrase search engine optimization was a spam message posted on Usenet on July 26, 1997.

Early versions of search algorithms relied on webmaster-provided information such as the keyword meta tag, or index files in engines like ALIWEB. Meta tags provided a guide to each page's content. But using meta data to index pages was found to be less than reliable because the webmaster's account of keywords in the meta tag were not truly relevant to the site's actual keywords. Inaccurate, incomplete, and inconsistent data in meta tags caused pages to rank for irrelevant searches. Web content providers also manipulated a number of attributes within the HTML source of a page in an attempt to rank well in search engines.

By relying so much on factors exclusively within a webmaster's control, early search engines suffered from abuse and ranking manipulation. To provide better results to their users, search engines had to adapt to ensure their results pages showed the most relevant search results, rather than unrelated pages stuffed with numerous keywords by unscrupulous webmasters. Since the success and popularity of a search engine is determined by its ability to produce the most relevant results to any given search allowing those results to be false would turn users to find other search sources. Search engines responded by developing more complex ranking algorithms, taking into account additional factors that were more difficult for webmasters to manipulate.