As to the question, the answer unfortunately requires some familiarity with Reddit and having been a regular user there for a while. /r/politics is the big one since it was a "default" community up until that concept was eliminated a while ago (basically it was automatically on the front page if you browsed the site while logged out, and if you made an account, you were automatically subscribed to it).
I bring them up, because they're the largest political community on the site, and had a level of privilege that comes with that.
CTR is used as shorthand for the pro-Hillary tonal shift in /r/politics that happened fairly rapidly[1], combined with fairly obvious botting[2]. While there's no proof that any particular organization was responsible for those posts, or that Reddit's owners tacitly permitted their behavior, CTR is to my knowledge the only organization who had social network promotion (beyond the usual writing their own obvious posts or buying ads) of Hillary Clinton as its goal, going to the point of addressing actual individuals. AFAIK, this is new.
[1]: https://www.thedailybeast.com/hillary-pac-spends-dollar1-mil...