Definition

SEO (Search Engine Optimization) is the process of improving the quality and quantity of website traffic to a website or web page from search engines. SEO targets unpaid traffic rather than direct or paid traffic. The better visibility your pages have in search results the more likely you are to garner attention and attract prospective and existing customers to your business.

What goes into SEO:
Quality of traffic: You can attract all the visitors in the world but if they are coming to your site because Google tells them you are a resource for Apple computers when you are actually a farmer selling apples, that is not quality traffic. Instead, you want to attract visitors who are genuinely interested in the products that you offer.
Quantity of traffic: Once you have the right people clicking through from those search engine results pages (SERPs), more traffic is better.
Organic results: Ads make up a significant portion of many SERPs. Organic traffic is any traffic that you do not have to pay for.