What is sweep picking?

I was looking round at some posts and notcied 'sweep picking' i have never heard of this before, so what is it?

Thanks Jowin

Here's a little something I wrote a few years ago.
http://www.wholenote.com
once there, click the lessons tab, and in the search box type in lesson# 1938 (make sure there is a space between the # and 1938. Click page one and it will give you a little insight on it and some real basic sweep exercises to play with. Once you get used to it, there are more advanced lessons on there to really get you sweeping