Social media is focused on the person first and foremost, internet forums are focused on a discussion topic.

Lemmy is a forum, Pixelfed is social media.

Youtube started as a sort of video forum, where the video was the main subject of discussion, this has changed to turn it into a social media site, where the content creator is in focus, and the content is secondary.

A decent rule of thumb is that if you are more interested in the creator than the content, then it is social media

With things like Facebook, X, etc. ‘advertising vehicle’ is probably the most accurate term.

“Forum” is more appropriate, and what we used to call non real-time communication tools online. Real-time is a chat room. Even tho forum would be appropriate for that, too.

a place, meeting, or medium where ideas and views on a particular issue can be exchanged.