SEO (search engine optimization) is a term that describes how websites get ranked in Google, Bing, Yahoo and other search engines, organically (i.e., without paying the search engines directly). The key focus of SEO is the overall quality of the website and how well it presents the information about itself and all of its individual pages.
SEO is critical in digital marketing, and webmasters and developers must keep it in mind when creating websites. SEO refers to the process of perfecting a website according to the ever-moving targets as set by the search engines and their black boxes of algorithms. Key things that matter for all search engines are indexability, content, site structure, relevance, links/citations and, overall, how a site provides the solution based on the user-intent implied by any given related query. SEO is the long-term marketing strategy for any given website and involves input and work from everyone in the organization including marketing, content production, website developers, front-end/user-interface designers and even internal product purchasers and engineers.