Search engine optimization (SEO) is the process of increasing the quantity or quality of traffic to a web-site from search engines, for example Google and Yahoo, through “natural” (also known as “organic” or “algorithmic”) search results. With the standard Google format, these will appear on the left-hand side of the page below the pay-per-click advertisements. In general, the higher a site appears in the search results list, the more visitors it will receive from the search engine. SEO companies will target different kinds of search, including image search, local search, and industry-specific vertical search engines, to give a web-site an improved presence within the search engines.

As a possible internet marketing strategy solution, SEO considers the method of how search engines generate their natural rankings and what the market will usually search for. Optimising a web-site primarily involves editing its content and HTML or other associated coding to both increase its relevance to specific keywords and to remove barriers to the indexing activities of search engines.

The acronym “SEO” also refers to “search engine optimisers,” a term adopted by an industry of consultants and advisors who carry out optimisation projects on behalf of clients, and by employees who perform SEO services in-house, i.e. within their own business. Search engine optimisers will typically offer SEO as a stand-alone service or as a part of a broader marketing campaign. Effective SEO may require changes to the HTML source code of a site. This means SEO tactics can be incorporated into web-site construction, development and design. The term “search engine friendly” may be used to describe web-site designs, menus, content management systems, images, videos, and other elements that have been optimised for the sole purpose of search engine exposure.

Black hat SEO or Spam-dexing is another class of techniques. SEO firms who use this technique will use methods such as link farms, keyword stuffing and article spinning that degrade both the relevance of search results and the user-experience of search engines. Search engines have now started methods to find sites which employ these techniques so that they can be removed from their indices and will not appear on that particular search engine.