SEO stands for search engine optimization, and it covers all the methods employed in generating traffic to your website from organic search engine results.
Search engines, like Google and Bing, present results based on a ranking system that looks at three main factors: relevance, authority, and popularity. SEO is the process of optimizing (the O in SEO) websites to rank well in these three factors for a given search. The end goal of SEO is to drive traffic to your website by ranking high on the search engine results page (SERP).
To achieve this goal, SEO looks at a wide range of on-page and off-page factors to determine how to improve the relevance, authority, and popularity of a website. This work encompasses the technical coding, creative content, and relative position of a website.