SEO (Search Engine Optimization) is getting your website to rank organically in the top search results. This is a long-term tactic that will continue to provide you traffic for years to come.
According to Moz, the first page of Google captures roughly 71% of search traffic clicks. Even more surprisingly, the first five search results on the page capture roughly 67% of clicks.
SEO has had a rough past. Many employed black/gray hat tricks to game the system. It worked for a while until google came out with a new algorithm (referred to as updates such as penguin, panda, etc.)
While many still try to "game" the system, I know that it's about quality links (not bought), good content to engage readers, and essentially how useful your website is to visitors. Even still, I perform an SEO website analysis for my clients, and identify areas of improvement, which could include site structure, on-page optimization, link-building opportunities, problematic load times, bounce rates, and much more.