Those would be sites that allow people to share images, videos, prose, etc. and network with all kinds of people globally. Your big names would be Facebook, X, Instagram, Truth Social, TikTok, Reddit, Discord, LinkedIn, Mastodon and so forth.How do you define social media?
(Of those, I have a LinkedIn account.)
I’d say image hosting sites- especially those that allow commentary & votes- are also social media, as are smaller message boards/online forums. But compared to the big ones? Generally, those are small potatoes.