To produce it short, you have 2 main different types of traffic: Google search traffic What is it?: organic traffic coming from search engines such as Google, Gmail, MSN Traffic is highly targeted Volume of traffic are often very high. people don't control it, you use robots to analyze your site and deliver some potential customers, you have to get indexed... without being de-indexed (again, you rely on yahoo policy and algorithms), short-term. Known Traffic (Actually, i know Search engine traffic is also sort of referred traffic, but let's put SE traffic in addition to the this category. Traffic provided by third party sites (other than search engines) and is because a "manual / human" action.