Shows how often a referrer (i.e., a website that links to your website) where a URL parameter was passed has been tracked.
Example:
A user clicks on a paid campaign at Facebook that is to which a URL parameter has been added:
If the URL parameter "wt_mc=facebook" is used as a data source of a campaign, this counts as "Campaign Source". If this is not the case (or if the link does not have a URL parameter), it is counted as "Organic Source".