Pick tapping (or pick trilling) is a legato playing technique for the guitar, in which the edge of the pick is used to sharply trill notes on the instrument's fretboard at fast speeds. Whilst trilling can be performed with the fingers of either the fretting or picking hand, using the pick enables faster speeds by means of 'vibrating' (or effectively seizing up) the wrist. The technique should not be confused with regular tapping, which always makes use of both hands and involves playing at least three or more notes.
A well-known example of pick tapping can be heard near the beginning of Randy Rhoads' guitar solo on Ozzy Osbourne's "Crazy Train", where rapid trills using the pick are performed on the third string whilst the left hand slowly bends and releases a fretted note lower down on the same string (the latter having an effect similar to that of a vibrato bar being depressed and released). Other examples include "Surfing with the Alien" by Joe Satriani, and various songs by DragonForce.