Search engine optimization (SEO) is the practice of increasing the amount and quality of visitors your website through organic and natural search engine results.
What goes into SEO? To understand what SEO really means, a few break that sentence down and look at the parts:
Quality of traffic. You can attract all the visitors in the world, but since they're arriving to your site because Google tells them you aren't a resource for Apple computers when really you aren't a farmer selling pears, that is not quality traffic. Instead you want to attract visitors who are genuinely enthusiastic about products that you offer. Variety of traffic. Once you have the right people clicking through from those search engine pages (SERPs), more traffic is way better. Organic results. Ads makeup a significant portion of many Search page results. Organic traffic is any traffic that you avoid have to pay for.