Direct, referral or organic traffic

Just trying to get my head around the ‘Direct’, ‘Referral’ and ‘Organic’ traffic classifications in Google Analytics. Basically ‘Direct’ is where there is no referrer header, e.g. user typed URL into address bar, clicked on link in email, etc. ‘Referral’ means some website referred the traffic, e.g. a link in an article on another website. ‘Organic’ means that one of a predefined set of search engines referred the traffic in response to a search.

Not sure how Google AdWords traffic is classified… I expect that would be ‘Referral’ as it’s not ‘Direct’ and not really ‘Organic’ either.