>>64790652people that think random youtubers or streamers are their friends. I guess it'd apply to any celebrity but you don't really see it with movie stars/athletes/etc. outside of the extreme end (think the bjork stalker) and it's way more commonly used to describe the relationship online personalities have with their audience.
problem is, it's specifically about one-sided relationships. It can absolutely apply even to the smallest vtubers if some schizo latches on to them even after getting told to fuck off, but in circles like these it's almost exclusively used incorrectly by people that don't know what they're talking about. Someone with 27 followers and 8 viewers that knows them by name and regularly has back and forth conversations with them isn't being parasocial. They're just being social.
This isn't to say that every viewer is a streamer's friend when you're watching smaller channels. it isn't that easy and of course everyone has their own definition of what a "friend" is, but even if they're only being polite to a random viewer there's still more going on than the cold, impersonal "chat" that you'd see in something like a holo/niji channel.