SEO consists of ...
improve the visibility of a website so that it appears in better search results organically. That is why this concept is also called natural positioning, organic positioning, search engine positioning, web positioning or, simply and given the relevance of this search engine, positioning in Google.
In this way, SEO is one more gear within digital marketing, along with other disciplines such as SEM (Search Engine Marketing), SMM (Social Media Marketing), Email Marketing, Web Analytics, etc.