I have two answers to What is Pinch Harmonic and How You Do It?

Short Answer:

Pinch harmonic is a sound produced by forcing the amplitude of the actual notes to be narrower, and that makes the frequency higher. Hence, the higher notes (usually major 3rd, and 5th, and an octave higher).

Harmonic itself can be produced by slightly touching a string and plucking it on top of the fret (not the bar). Because even when making a note on the guitar, the fret is actually what determines the pitch of the note, not the wood part we’re pressing on.

Longer Answer:

Slight history Of Pinch Harmonic:

In classical (nylon) guitar playing, the guitarist plucks the string right on the fret and lightly touch the string to block the string’s movement. The gesture is the same as a pinching finger. Hence, the name pinch harmonic is created.

In Modern Rock Era:

In a more modern era, this trick becomes even more popular. Thank’s to George Lynch and Eddie Van Halen who with their unique playing and killing whammy bar technique brought pinch harmonics to the younger audience through rock music in the wave of punk and disco.

Also, read Eddie Van Halen Interview.

However, electric guitar players are not (only) using the same plucking technique as the nylon guitar players. Instead, the sound is produced by holding the string using the thumb right after the string was struck. The pinch harmonic is not produced on the fretboard alone, but mostly by doing it above the pick-ups area. This allows the guitarists to produce pinch harmonic faster by moving only their right arms.

This is how the same theory and idea of pinch harmonics applied differently:

This technique later becomes popular by the name Squeal. ’cause it sounds like a pig.

Here is an example how a pinch harmonic produced using the string only and not fretted notes:

And this is the perfect example of how squeal applied to heavy metal:

I hope this article explains well about What Is Pinch Harmonic and How You Do It.

Also, read 30 cool guitarists.