Eddie Van Halen is credited with popularizing this technique. Rather than picking the string with the plectrum, you tap the first or second finger of your right hand against the string on the fretboard. The pressure of the tap creates a note. By hammering your left hand fingers down on the same string, you create a rapid sequence of notes. The guitar solo at the beginning of "Hot for Teacher" by Van Halen features a prominent example of two-handed tapping. Randy Rhodes' solo in "Crazy Train" by Ozzy Osborne features the technique as well.
Instead of picking notes individually, you drag your pick down across the strings while fretting with your left hand. This technique is challenging and requires accurate timing. Because the pick is traveling in one direction, the string changes appear seamless. The second half of the solo in "Get the Funk Out" by Extreme is characterized by a series of major arpeggio sweeps.
String bending lets you increase the pitch of a note without changing frets. By pushing your fretting finger upward, you increase the tension of the string. The roots of string bending are in blues music, but the technique is popular in rock, pop and heavy metal. There are multiple types of string bend techniques, including double-stop bends, in which you pick two strings and bend one so that the harmony changes as the pitch of the bent string increases. Unison bends are similar, but the static note is the same pitch as the note to which you bend.
This involves holding your pick in a way that lets your thumb make contact with the string as you pick. The extra contact creates a harmonic since the string is ringing and is touched immediately afterward. The harmonic creates a distinctive "squealing" sound. Zakk Wylde of Black Label Society frequently incorporates this technique into his solos.
With a pinch harmonic still ringing, depress the string with the tremolo arm. The rapidly descending pitch of the squealing harmonic approximates a diving sound--hence, the name. The late "Dimebag" Darrel Abbot of Pantera and Damage Plan used this technique in a lot of his solos, notably at the very end of the solo in the Pantera song "Walk."