PICK SLIDE: Either starting at the bridge end or nut end of the fretboard place your pick at a 90 degree angle to the strings and scrape the edge of the pick along the length of the thicker wound strings. The sound is produced by the edge of the pick edge moving over the small bumps on the wound string.
This effect is usually played when the guitar is distorted or overdriven and will most commonly precede or end a solo. A good example of a pick slide it the intro to the solo on Smooth Criminal - Alien Ant Farm.