SEO or Search Engine Optimisation is the name given to the activity of improving your search engine rankings, in the search results for Google, Yahoo, Bing etc…. To gain strength for your website in the search engines and to excel in the rankings your pages need strength (authority). Authority is mostly measured by analyzing the number and quality of links from other website pages to yours. In simple terms the more power you have the better.
You will want Search engine optimisation (SEO) if you are focusing on getting your website to the highest possible rank in organic (non-paid) search engine results. Ideally number 1 on page one . It has been proven that most people searching for a service/product never go past page one (do you). Therefore the higher up the rankings you are, the more trusted your brand/company becomes, and the more traffic you gain to your website. This unfortunately means that if you are ranking on page 2 for keywords relating to your business, you will not be gaining much traffic and your website will not be performing efficiently for you.