The specific source that you are sharing the link to such as Twitter, NYTimes.com, email newsletter, Route 9 billboard, Channel 5 news, etc.
The advertising or marketing medium where the link is being placed such as website, email, cpc, print, social, radio, etc.
Give your campaign a name so you can differentiate it from other similar campaigns. Keep it short but identifiable.
Similar links within the same campaign? Use this to differentiate them.
Running the same campaign but perhaps with different keywords or hashtags? Put them here.