SEO or Search Engine Optimisation is the name given to activity that attempts to improve search engine rankings.
In search results Google™ displays links to pages it considers relevant and authoritative. Authority is mostly measured by analysing the number and quality of links from other web pages.
In simple terms your web pages have the potential to rank in Google™ so long as other web pages link to them.
Search Engine Optimisation or SEO is the simple activity of ensuring a website can be found in search engines for words and phrases relevant to what the site is offering.