Heads up, Creators: On Dec 13-14 you may see a noticeable decrease in your sub count as we remove spam subscriptions. If spam is removed, you'll see a YouTube Studio alert: https://goo.gl/qGDBvX This should help give you confidence that the subs you do have are real fans!
Spam are subscribers gained through artificial means, such as purchasing subscribers through a third party service. We don't remove legit subscribers from the sub count. For example, if you're subscribed to a channel and you haven't watched in a while, you'll still be subscribed.