Subscription

A Subscription is a feature whereby one receives the latest additions to a YouTube user's videos, a YouTube tag, a YouTube search term or a YouTube playlist. There are two types of subscribing to videos:


 * clicking the red "subscribe" button at either the top right or top left of the page
 * going to "my subscriptions" and entering a tag or two to the search box that says "Subscribe to Tags", and hitting subscribe.

A user cannot subscribe to another user's subscriptions, as those are kept private.

RSS
The above is separate from subscribing to an RSS feed which syndicates YouTube videos to applications and websites outside the site. One can syndicate user playlist subscriptions as an RSS feed, however.

Channels by Subscription
The following is a chart featuring a list of the 250 most subscribed YouTube channels (Updated December 13, 2019). This list will not include any terminated or deleted channels, nor channels with their subscriber count hidden. However, channels that have seen the recent purge in subscribers (Justin Bieber, Katy Perry, etc.) will be included in this list because it is the subscriber count shown on YouTube. Even VEVO channels, which have been blocked from gaining subscribers, will be included in the list as well. (Socialblade.com)

On September 9, 2019, YouTube changed their API so that viewers can only see abbreviated subscriber counts. The last three placements of a subscriber count are only visible. (Ex: 24,186,079 to 24.1M) The list will now only show abbreviated subsciber counts.