Search engine optimization (SEO), a subset of search engine marketing, is the process of improving the volume and quality of traffic to a web site from search engines via "natural" ("organic" or "algorithmic") search results. SEO can also target specialized searches such as image search, local search, and industry-specific vertical search engines.
SEO is marketing by understanding how search algorithms work and what human visitors might search for, to help match those visitors with sites offering what they are interested in finding. Some SEO efforts may involve optimizing a site's coding, presentation, and structure, without making very noticeable changes to human visitors, such as incorporating a clear hierarchical structure to a site, and avoiding or fixing problems that might keep search engine indexing programs from fully spidering a site. Other, more noticeable efforts, involve including unique content on pages that can be easily indexed and extracted from those pages by search engines while also appealing to human visitors.
The term SEO can also refer to "search engine optimizers," a term adopted by an industry of consultants who carry out optimization projects on behalf of clients, and by employees of site owners who may perform SEO services in-house. Search engine optimizers often offer SEO as a stand-alone service or as a part of a larger marketing campaign. Because effective SEO can require making changes to the source code of a site, it is often very helpful when incorporated into the initial development and design of a site, leading to the use of the term "Search Engine Friendly" to describe designs, menus, content management systems and shopping carts that can be optimized easily and effectively.
We define SEO (Search Engine Optimization) and SEM (Search Engine Marketing) as follows ...
SEO = Optimizing a Web page for a set of keyword phrases for the organic (free) listings.
SEM = Optimizing a set of keyword phrases for the pay-per-click (paid) listings.