Selecting “All Traffic Sources” from Google Analytics left-side navigation will show you a table listing the most active traffic sources and their medium. Direct traffic, as you would expect, has a medium of “none.” Traffic from Facebook, as an example, will have a medium of “referral.” Search engine traffic will have a medium or “organic” or “CPC” as described above.
The term “organic traffic” is used for referring to the visitors that land on your website as a result of unpaid (“organic”) search results. Organic traffic is the opposite of paid traffic, which defines the visits generated by paid ads. Visitors who are considered organic find your website after using a search engine like Google or Bing, so they are not “referred” by any other website.