Colorful simple bracelets worn mostly by teens. I used to have some when I was a kid, and now I'm a teen and I have a bunch more. They're also known as 'sex bracelets', that means if someone brakes a certain colored jelly bracelet (which is hard to do in my opinion), they have to do what the color means. But they're just mostly worn for fashion.
It's common to see them being worn by scene kids (or styles like scene).
You could probably find them just about anywhere, but I got mine at Hot Topic.
girl 1: I love your jelly bracelets!
girl 2: Thanks! I have a bunch more.
girl 1: Ooh! Can I have one?
girl 2: Sure, but make sure no one brakes it.