Expression pedals & Wah pedals

Can someone tell me what the difference is?
I have a Wah pedal, and was told that an expression pedal would be nice to have too.

A wah pedal (Crybaby or something) is a wah pedal. It's fine. You press it to make it work. An expression pedal is just that.. it's the elongated rectangle (pedal) that you press and adjust to make sound. It's basically the same. You can also use an expression pedal for volume swells. See ya--Rich

I see. Well, I have a vox wah pedal.
I don't think I'll get the expression anytime soon.
Thanks again, HawkV182