Channels
Channels are customizable feeds that allow you to create unique experiences by segmenting your content. While the home feed encompasses all the content you follow on a given site, a collection can do the same but for a select set of content. These are designed to let you have various sorted content-centric feeds which you can jump between.
Channels can be private (only you can view the feed) or public (discoverable, viewable and followable by other users).
Channels can include: users or tags. All the content posted by those users or using those tags will show up in that collection.