SEO is the abbreviation of “Search Engine Optimization”. It is a process to optimize a website to suit search engines and users needs. The ultimate goal for SEO is gaining higher ranking in Search Engines and increase user experiences
According to BBC news, When do online searching in search engines, 90% of people will go through 3 pages and 60% of people will stop on 1st page before giving up. (survey by Jupiter Research and marketing firm iProspect). It means that if your website rank higher in search engines, it will have higher chance to get noticed by the visitors and interests group.
However, We could not over emphasize on Search Engines needs and omitted the needs of searchers (the users). People need fast, user friendly and content rich website. Even in Google Ten Things, the rule #1 is : Focus on the user and all else will follow. (see below picture ) Meaning that you need to build a website that increase user experiences, and eventually Google will rank your website high.
In short term, Optimize your website to suit search engine requirements; In long run, Optimize your website to increase user experiences.
In General, SEO includes on-page optimization and off-page optimization :
On page optimization : Optimize the title tag, meta tags , images , rewrite-URL and anythings that involve direct modification on your website content.
Off page optimization : Building backlinks (links that point back to your website) which including blog writing, article submission, directories submission; as well as web hosting reliability, website loading speed and anythings that not direct related to your website content.
However, with the increase of the complexity of the internet and Google algorithm update, Other factors such as bounce rate, mobile friendly are take into account too.