Sweep-Picking.org

In theory, the technique is quite simple…however in practice it’s pretty tricky and takes a lot of practise.

Basically, instead of picking each individual string, you "sweep" accross them in a fluid movement. Your right hand should be going across the strings as if you were slowly strumming a chord, whilst your left hand fret’s the single notes in the same way as you would normally pick them out. So, you need to make sure your left hand is dead in time with the right so you are fretting the notes as your right hand hits the strings. By sweeping accross them, you save a lot of time, hence the ability to play very fast using a sweep.

If it still makes no sense, type "sweep picking" into google, and you’ll find loads of tutorials.