The Discord communication platform has started testing the functionality they call "Watch Together". It's actually about integrating YouTube into Discord itself, which would allow users to share a specific video on YouTube on a specific server.
Such a thing is technically already possible but provided that one of the users streams YouTube to others from their browser. The Watch Together option would allow all participants to add videos from YouTube to a shared playlist.
Discord transparently emphasizes that the Watch Together option will be subject to occasional advertisements on YouTube.
This announcement probably has something to do with the fact that YouTube recently started fighting Discord bots that played music to users via YouTube. The contentious issue was that Discord users were able to consume content from YouTube without actually being on YouTube, and this is against the rules of use of YouTube.
Now, music from YouTube will be able to be listened to again on Discord's servers - only in a slightly different form that will be a less automated process. And much more closed.
See Also: How and why to start using Discord?