This is a forum, AKA a 'bulletin board', and would have been universally recognised as such in the glory days back before what we now call 'social media' existed in anything like its current form.
They're online environments (aka media) for discussions (aka a form of social interactions).
"Social media" is just the mass market name for forums.
Edit:
I'm kind of flattered that someone created a new account just to nitpick a comment of mine :-))
Keep on keeping on, senormenor: https://xkcd.com/386/