New to Forum. But what is this thing on my cable?

I notice that on some USB cables, there is a, um, what looks like a swollen area wrapped around the wire near one end (or both ends). My HTC Droid Eris has a USB cable that has one on it. It looks like a cylinder of some kind. What is it and what does it do? Thanks.

Is this sorta what your talking about could be this.

Ferrite Chokes

That's it

Thank you. Now I know.