Reddit engagements are a sum of upvotes and comments.
For new threads that are created around a link to an article, Reddit users can vote up the link and/or comment in the thread. The more engagement a link receives, the more likely it will be pushed to Reddit's FrontPage.
(Note: Reddit users can also vote down a link. This data is not tracked in BuzzSumo's calculation).
To learn more about how to leverage Reddit in your content marketing strategy, check out these helpful tips.