question about usernames?

[ilovepsyschonaut4]

I was curious that when I have to choose a "unique" username, does this mean only on my social media accounts or does this mean usernames that someone else has used before on another site? I chose one I couldn't find online but I would like to make it something else and I'm worried I'll get banned/warned since another account has used it before. (Not on this site)

 

[U. A.]

Just don't use a handle that you use anywhere else and that isn't in use by anyone else here.
Ideally it's also not one that formerly was in use by someone active here.