TappingTapping is a playing technique (generally associated with electric guitar playing, though the technique can be performed on any fretted instrument) executed by using the fingers of the picking hand to tap behind the frets of the fingerboard, sounding notes. Tapping (also known as a two-hand hammer-on), performed in conjunction with normal fingering by the fret hand, facilitates the construction of note intervals that would otherwise be impossible using the fretting hand alone.
The perhaps most famous employment of tapping is the short piece "Eruption" on the first Van Halen album, which features very fast tapping runs and formed the blueprint of heavy metal lead playing throughout the 1980s. Eddie van Halen is generally attributed with "inventing" tapping, but this is not accurate as the technique has existed in some form or another for many decades; this erroneous attribution is probably the result of the wildfire-like spread of the technique after Van Halen popularized it.
A related technique is "tapped harmonics", where the fret hand acts as a barre, while the harmonic is tapped. Eddie van Halen also popularised this technique, using it in the acoustic guitar solo "Spanish Fly".
Perhaps the most spectacular technique related to tapping is the "touch guitar" technique used by Stanley Jordan, where the pick hand is used to play lead while rhythm is simultaneously played with the usual fret hand.