Or better known as Search Engine Optimization...

(SEO ) is the work done to a website, both on and off site, to help it gain a higher display rank (SERP), when someone types in a keyword related to your product or service. Getting a higher seo score is just science with a touch of art.

People See Design, Computers See Optimization
Because of design and optimization, the majority of the websites on the internet are virtually invisible to someone trying to find them. They're known as Stealth Websites. On a well designed site, search engine optimization is like the rocket booster on the Space Shuttle, taking it into orbit. Striking that balance between search engine algorithms and reader useability, and being able to bring relevant traffic is where the work is. If the searcher feels like they targeted you, when in reality you targeted them, that's the reward of search engine optimization.

The Two Sides of Optimization:

On-Page (site) Optimization (SEO)
On-page optimization, SEO, are the elements that are done to the actual website to make it search engine friendly. These include:

Off-Page (site) Optimization (SEO)
Off-page optimization, SEO, are the elements that are done to the outside of the actual website to make it search engine friendly. These include:

Off-site optimization, seo, breaks down into just one word; Backlinks. The primary purpose of all the above is simply backlinks.

A veteran of the search engine optimization industry once said "whoever dies with the most links, wins." That statement crystalizes the importance of backlinks.