This is from an old steel Schwinn roadbike. I can't seem to figure out how to describe this well enough to get useful search results from Google. So, how do I remove this ?freewheel?, and also, how would I have searched for information about it?

Image:
https://docs.google.com/open?id=0BxhSJoGQbQSKeDc0QVZlam41eEU


Thanks,
Marc Dillon