Cosplay ball question

I'm kind of confused about the ball thing, my friends say you just come in formal wear...?
Like, as in not even cosplay, and I just need someone to explain to me exactly what it is because I really don't understand xD;

Hi Mari,

Tradionally, peole dress up formally for balls. Cosplay balls follow this by encouraging people to wear formal clothing from characters.

This isn't essential however, and you won't be turned away if you just turn up wearing normal clothing.

JC11

So for example, I could cosplay a character who's clothes are generally pretty formal?
Or I could come as like...myself in formal wear? xD;

Say you're cosplaying someone from an anime series (obviously >.<) and they have a special formal outfit only saw in one volume of manga or one episode (most characters do, just for the fanservice of seeing them in a special pretty dress or suit) you could come as that!

Even better you could cosplay as the character in their normal outfit for the first day then come in the exclusive formal outfit for the ball.

I think I get it now...
Unfortunately, I still don't know who I'm cosplaying so I can't know whether they have a formal outfit ;;
I've had various plans to cosplay in groups with friends but I've been ditched multiple times and now two of them have decided to cosplay Black rock shooter together and I'm alone XDD

Aw, that sucks! >.<