I forgot to include a link there so that’s my bad. I was referencing Signal, which is an automatic tweeting tool:

Signal Review: Tool That Auto-Tweets Your Medium Articles on a Schedule

Email, IM, and direct refers to traffic not originating from Medium’s site, including email links (i.e. me, sending you an email with a link to my article), IM would be links sent through chat functions or messengers (Google Chat, Slack, etc.) and direct is someone going straight to the article, which could be someone manually entering the URL, finding the article in their history/browser suggestions, or through their page bookmarks.

Sorry if this wasn’t clear!